Previously, some modules used BH_<Module> prefix in the names of static
functions (some used just <Module> prefix). Now every static function
should start from lowercase.
Added initial implementation (or wrapper) of the threading library.
It's rather basic, but should work for most of the tasks.
Unfortunately, spinlock implementation relies on GCC/Clang compiler
built-ins (or in-worst-case-scenario on Win32 - InterlockExchange).
In the future, I should revisit this code and fix/reimplement some stuff
(or add support for Windows XP).
