An attempt to normalize some of the function names in build.zig. Normalize add*Dir to add*Path. Also use "Library" instead of the "Lib" abbreviation.
The PR does not remove the old names, only adds the new normalized ones to faciliate a transition period.
This commits permits passing in static archives using the system
lib flag `-la`. With this commit, `zig ld` will now look firstly for
a dynamic library (which always takes precedence), and will fall back
on `liba.a` if the dylib is not found. The static archive is searched
for in the system lib search dirs like the dylibs.