Removed out-of-date sentence from README.
Mentioning YCM_CORES var in FAQ when out of RAM.
Added a unicode test for OverlapLength()
Custom identifier support now done.

This commit is the YCM-client part of the support. The ycmd support is
already done.

We now need per-language identifier regexes in ycmd (see
identifier_utils.py). There's some for HTML, CSS and the generic regex
that was used for everything until now.  Pull requests welcome for other
languages.

Fixes #86.