[C] Highlight stddef.h and stdint.h types

[obskyr]

As it stands now, types and values from stdbool.h (bool, _Bool, true, and false) are highlit, but not those from stddef.h (except NULL) and stdint.h. As those are very commonly used (often almost entirely replacing normal integer types), not having them highlit commonly results in slightly harder-to-read code. The keywords in question are:

• stddef.h
  • size_t, wchar_t, ptrdiff_t
  • perhaps offsetof
• stdint.h
  • int8_t, int16_t, int32_t, uint8_t, uint16_t, and uint32_t
  • int_least8_t, int_least16_t, int_least32_t, int_least64_t, uint_least8_t, uint_least16_t, uint_least32_t, and uint_least64_t
  • int_fast8_t, int_fast16_t, int_fast32_t, int_fast64_t, uint_fast8_t, uint_fast16_t, uint_fast32_t, and uint_fast64_t
  • intptr_t and uintptr_t
  • intmax_t and uintmax_t