Added functions to lib

[MrLego8-9]

Added functions from libC : memchr, memrchr and strstr Added from libmath :

• Macros : HUGE_VAL, HUGE_VALF, INF, INFINITY and NAN
• utility functions : isnan(), isinf(), fabs() and fabsf()

[pitust]

Please fix your commit messages -- they should be conventional commits

Your commit messages should also be under the 72 character limit that git prefers

Also, i'm pretty sure those math functions were there for a reason.

[pitust]

Also, please squash the commits together if they are related and don't work alone