Include version number in SONAME

The SONAME should include the version number.

(closes issue ASTERISK-22254)

Signed-off-by: David M. Lee <dlee@digium.com>
Remove DESTDIR from pkgconfig file.

Paths in the pkgconfig file are relative to DESTDIR, so it should not be
prepended to the paths in libpjproject.pc.

dlee: patch slightly modified; removed an extra $ in $$(libdir)

(closes issue ASTERISK-22253)
Signed-off-by: David M. Lee <dlee@digium.com>