[READY] Use non-capturing group in JavaScript identifier regex

In PR #643, we added a regular expression with a capturing group for JavaScript (and TypeScript) identifiers. Unfortunately, this makes [`re.findall` returns matches of this group instead of the whole pattern](https://docs.python.org/2/library/re.html#re.findall). Since this function is used in `ExtractIdentifiersFromText`, it breaks the extraction of identifiers in JS and TS files. We fix the issue by replacing the `(...)` pattern with `(:?...)`.

Added a test that fails without the fix:
```
AssertionError: ['var', 'foo', 'require', 'bar'] != ['v', 'f', 'r', 'b']
```

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[READY] Update readme for compilation database support

# PR Prelude

Thank you for working on YCM! :)

**Please complete these steps and check these boxes (by putting an `x` inside
the brackets) _before_ filing your PR:**

- [X] I have read and understood YCM's [CONTRIBUTING][cont] document.
- [X] I have read and understood YCM's [CODE_OF_CONDUCT][code] document.
- [X] I have included tests for the changes in my PR. If not, I have included a
  rationale for why I haven't.

> only changes docs

- [X] **I understand my PR may be closed if it becomes obvious I didn't
  actually perform all of these steps.**

# Why this change is necessary and useful

This change:
 - updates the c-family completer documentation to describe the built in support for compilation databases added in ycm-core/ycmd#680
 - explains more about why ycmd needs compiler flags, and how to go about providing them
 - recommends using a compilation database (as that seems to be the fashion)
 - standardises formatting for `NOTE` (it was inconsistent before)
 - states that the preferred installation method is `install.py` (rather than the full installation instructions)
 - update the vim doc
 - update the ycmd submodule

### ycmd update release note

- ycm-core/ycmd#678 - Bump Boost version to 1.63.0
- ycm-core/ycmd#686 - Update JediHTTP for Python 3.6 support
- ycm-core/ycmd#684 - Fix JavaScript identifier regex
- ycm-core/ycmd#680 - Automatically load a compilation database if found

[cont]: https://github.com/Valloric/YouCompleteMe/blob/master/CONTRIBUTING.md
[code]: https://github.com/Valloric/YouCompleteMe/blob/master/CODE_OF_CONDUCT.md

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