Fix compilation with Lua 5.1
Add new State constructor allowing to work with existing lua_State.
Change tabs to spaces and move constructor getting lua_state to the right place.
Merge pull request #44 from rafalh/ctor-lua-state-patch

Add new State constructor allowing to work with existing lua_State.
Merge pull request #43 from rafalh/lua51-support

Fix compilation with Lua 5.1
Merge changes from upstream.
Add MetatableRegistry to support binding registered metatables to userdata.
Delete unnecessary comments in MetatableRegistry.h
Fix userdata implementation and add relevant new tests.
Merge branch 'master' of https://github.com/jeremyong/Selene
Throw LuaError exception if Lua code failed (instead of crashing).