[DOCS][SQL] Add a Note on jsonFile having separate JSON objects per line

* This commit hopes to avoid the confusion I faced when trying
  to submit a regular, valid multi-line JSON file, also see

  http://apache-spark-user-list.1001560.n3.nabble.com/Loading-JSON-Dataset-fails-with-com-fasterxml-jackson-databind-JsonMappingException-td20041.html

Author: Peter Vandenabeele <peter@vandenabeele.com>

Closes #3517 from petervandenabeele/pv-docs-note-on-jsonFile-format/01 and squashes the following commits:

1f98e52 [Peter Vandenabeele] Revert to people.json and simple Note text
6b6e062 [Peter Vandenabeele] Change the "JSON" connotation to "txt"
fca7dfb [Peter Vandenabeele] Add a Note on jsonFile having separate JSON objects per line

(cherry picked from commit 1a9e35e57ab80984b81802ffc461d19cc9239edd)
Signed-off-by: Michael Armbrust <michael@databricks.com>
[SPARK-4847][SQL]Fix "extraStrategies cannot take effect in SQLContext" issue

Author: jerryshao <saisai.shao@intel.com>

Closes #3698 from jerryshao/SPARK-4847 and squashes the following commits:

4741130 [jerryshao] Make later added extraStrategies effect when calling strategies

(cherry picked from commit dc8280dcca7b54793a3db644f74fd33460960d4a)
Signed-off-by: Michael Armbrust <michael@databricks.com>
[Release] Major improvements to generate contributors script

This commit introduces several major improvements to the script
that generates the contributors list for release notes, notably:

(1) Use release tags instead of a range of commits. Across branches,
commits are not actually strictly two-dimensional, and so it is not
sufficient to specify a start hash and an end hash. Otherwise, we
end up counting commits that were already merged in an older branch.

(2) Match PR numbers in addition to commit hashes. This is related
to the first point in that if a PR is already merged in an older
minor release tag, it should be filtered out here. This requires us
to do some intelligent regex parsing on the commit description in
addition to just relying on the GitHub API.

(3) Relax author validity check. The old code fails on a name that
has many middle names, for instance. The test was just too strict.

(4) Use GitHub authentication. This allows us to make far more
requests through the GitHub API than before (5000 as opposed to 60
per hour).

(5) Translate from Github username, not commit author name. This is
important because the commit author name is not always configured
correctly by the user. For instance, the username "falaki" used to
resolve to just "Hossein", which was treated as a github username
and translated to something else that is completely arbitrary.

(6) Add an option to use the untranslated name. If there is not
a satisfactory candidate to replace the untranslated name with,
at least allow the user to not translate it.
[Release] Cache known author translations locally

This bypasses unnecessary calls to the Github and JIRA API.
Additionally, having a local cache allows us to remember names
that we had to manually discover ourselves.
[Release] Update contributors list format and sort it

Additionally, we now warn the user when a duplicate author name
arises, in which case he/she needs to resolve it manually.
[HOTFIX] Fix RAT exclusion for known_translations file

Author: Josh Rosen <joshrosen@databricks.com>

Closes #3719 from JoshRosen/rat-fix and squashes the following commits:

1542886 [Josh Rosen] [HOTFIX] Fix RAT exclusion for known_translations file

(cherry picked from commit 3d0c37b8118f6057a663f959321a79b8061132b6)
Signed-off-by: Josh Rosen <joshrosen@databricks.com>