Build system suggestions

-`pkg-config ...` gets run every time (twice), please use $(shell pkg-config ...) to evaluate and store the result.

-Don't mess with the systems CFLAGS, esp. do not overwrite values.
Use += instead of =.
- Respect LDFLAGS, add $(LDFLAGS) before $(LIBS)

Awesome app! This is so going to Gentoo/Linux main repo!