Use a single BASIC_TYPE token for basic types, while using its string representation as a type name. This also fixes incorrect type used previously for __uint128_t, __int128_t, __uint128, __int128, and _Float128 (they have been mapped to int and float respectively).
Also avoid mapping bool and _Bool to gboolean as those are distinct types and generally ABI incompatible. Fixes issue #202.
After this changes, when _Bool, _Float* or _int128 types are used as a part of public API, g-ir-scanner will produce warning about unresolved type. This is appropriate given that they are currently inexpressible in GIRepository format.