- keep supporting regex for old endpoint.
- use reserved keyword for removed property in grpc

- adds avg,min,max,top,bottomk,stddev,stdvar,count
- updates api documentation
- adds tests

Improve yacc & go lexer to understand duration
Remove support for regexp in all queries
Clean up querier and logselector

Currently, it's difficult to determine what permissions Loki needs to operate against S3 and DynamoDB from the provided documentation. This commit adds the permissions necessary to operator Loki, to provide admins guidance on how they can run Loki with the least possible privilege.

The journal scrape config in promtail has been updated to support
a "max_age" field. max_age determines the oldest journal entry
promtail will read when starting the journal reader. When
unspecified, max_age defaults to 7h.

Even if a position in the journal is saved in the promtail
positions file, that position may be ignored if the entry corresponding
to that position is older than the max_age cutoff time.

Example promtail config for getting up to the last 12h of journal
entries:

  server:
    http_listen_port: 9080
    grpc_listen_port: 0

  positions:
    filename: /tmp/positions.yaml

  clients:
    - url: http://localhost:3100/api/prom/push

  scrape_configs:
  - job_name: journal
    journal:
      max_age: 12h
      path: /var/log/journal
      labels:
        job: systemd-journal
    relabel_configs:
      - source_labels: ['__journal__systemd_unit']
        target_label: 'unit'

adding the beginnings of the release doc with steps, fixing a bug in the release_prepare.sh script and tweaking the output based on the current process.

Fix link format

`from: 0` throws
```
level=error ts=2019-08-07T12:02:15.385981107Z caller=main.go:48 msg="error loading config" filename=/etc/loki/local-config.yaml err="parsing time \"0\" as \"2006-01-02\": cannot parse \"0\" as \"2006\""
```

`store: dynamo` throws:
```
level=error ts=2019-08-07T11:59:01.688427565Z caller=main.go:71 msg="error initialising loki" err="error initialising module: table-manager: Unrecognized storage client dynamo, choose one of: aws, cassandra, inmemory, gcp, bigtable, bigtable-hashed"
```

update retention section in docs to recommend retention to be twice the duration of periodic table

* Use single quote to avoid escaping regex

Adds an example of how to setup the `GRAFANA_ADDR` environment variable when not using Grafana Cloud but rather a local or otherwise hosted instance of Loki

add a Name() method to the stage interface so that debug logging can show you the name of the pipeline stage which just processed the log
remove some unnecessary logging around fsnotify events we don't care about and saving positions
Make the Processing Log Lines doc a first class citizen, I reference this a lot and currently it's hidden behind 3 clicks

Support for reading systemd journal entries has been added. 
promtail will look for a job in scrape_configs with a journal key 
to activate the journal target. 

If GOOS=linux and CGO_ENABLED=1, promtail will now require 
libsystemd headers to be available for building. If GOOS is not 
linux or CGO_ENABLED is not 1, journal support will be unavailable
and a log message will be printed warning the user that their config 
file has journal tailing configured without it being built into promtail. 

See docs/promtail-examples.md for a concrete example of 
using journal support. 

Other structural changes made: 

  1. Ability for checking if scrape.Config.ServiceDiscoveryConfig is 
     non-zero has been added. 

     This was chosen over making ServiceDiscoveryConfig a pointer
     as yaml.v2 cannot parse an inline struct into a pointer value. 

  2. Updated pipeline logger component name to journal_pipeline and
     file_pipeline for JournalTargetManager and FileTargetManager
     respectively.

  3. The positions file will now store positions as strings instead of 
     integers. Existing positions will be read in properly but written out 
     as strings the next time the positions file is saved. This is done to 
     be able to store the journal cursor, which is a string. The positions 
     API has been updated to support reading in the old integer values 
     and the new string values. 

* Query label values and names are now fetched from the store.

A time range is now required by the /api/prom/label with a sane default (6 hours from now).

* fix http querystring and update doc

* update vendor

* rebased

removed helm entry in scrape_config.sh because there doesn't seem to be anyway to make it work with new pipeline config

* loki chart deployment.yaml: Only set JAEGER_AGENT_HOST if set.

* docs/troubleshooting.md: Fixed variable name for chart option.

* Bumped loki chart version for variable fix.

Mentioned in title. To save new beginner's time, provide one config example for use Cassandra as Index Storage.