OmniSharp completer error message using incorrect naming format

The not found message used to instruct users on how to install the OmniSharp completer was using an underscore while the argument to the install script uses a hyphen. The message now uses the correct naming format.
flake fix and readme update
Merge pull request #512 from ciwchris/patch-1

OmniSharp completer error message using incorrect naming format
Some minor fixes
Merge https://github.com/Valloric/YouCompleteMe
Merge pull request #509 from Chiel92/master

Goto definition support for C# completer
Refactoring out TU storage into own class

This makes the code more readable, maintainable and robust since we're now
encapsulating the mutex to filename_to_translation_unit_.
Some minor refactoring of TU store
Ensuring TUs expire when compilation flags change.
Now parsing file on every normal mode cursor move

This is still fast & efficient because if we detect that the buffer hasn't been
changed (by examining b:changedtick), the parse doesn't proceed.

In effect, we now make sure we parse the file after every change to the buffer
as soon as that change happens. This means that compilation error feedback will
now be much, MUCH quicker.
Fixing bizarre compilation error on recent clang
Fix boost compilation issue with glibc 2.18
extra conf path handling now OS-agnostic

It used to work incorrectly on Windows.

Fixes #490.
Should compile on MinGW-64 now

Fixes #489.
Minor whitespace changes
Adding a script for easy BoostParts updating
Updating to Boost 1.54
Fix boost compilation issue with glibc 2.18
Ident collector handles escaped starting quotes

Previously, it would consider \"foo\"bar" as a slash and a "foo\"bar" string and
this would screw up tracking of quotes in the file.

Fix #535.
Refactoring a big test into smaller tests