implemented ldata_toptr()
removed unecessary data obj checking on metamethods
added a compat layer with Lua 5.2 to use luaL_testudata()
added obj/ on .gitignore
improved test.c
added test on .gitignore
returning size = 0 if ptr is NULL on ldata_toptr()
added ldata_toptr() test on test.c and gone to assert()'s
removed warnings
Merge branch 'master' of https://github.com/lneto/lbuf