Turn on compiler errors

[juntuu]

• added -Werror, -Wall and -Wextra flags
• fixed unknown attribute inline to always_inline
• added -ferror-limit for clang in stead of -fmax-errors
• organised warning flags, and treating warnings as errors in logical sections

This might resolve #90 and also resolve #89

Lets see if it builds also on linux, I only tested on mac locally.

At the moment the following warnings (and counts) are generated (and ignored from errors) by gcc on the ci, but not clang on osx:

   2 -Wsequence-point
   3 -Wstrict-overflow
   4 -Wlogical-not-parentheses

[juntuu]

Seems like there are quite different settings for gcc/clang regarding disabled warnings.

I'll continue with this a bit, and see if I get it working.