avoid .. in includes
put the header to subdir already, while i am at it
add .pc file
produce also .tar.bz2 and .tar.xz
package license
headers used from a public header must be public too

Otherwise there is no way to build against system-installed lib, as
there would be missing headers.
improve handling of .pc
name API functions consistently
fix operator precedence
free expects void*
different enum
get the right return type
return value from the right enum