release libmypaint 1.4.0

This release adds some additional features
and bug fixes.

Author: briend

configure.ac

@@ -5,7 +5,7 @@ AC_PREREQ(2.62)
 m4_define([libmypaint_api_major], [1])
 m4_define([libmypaint_api_minor], [4])
 m4_define([libmypaint_api_micro], [0])
-m4_define([libmypaint_api_prerelease], [alpha])  # may be blank
+m4_define([libmypaint_api_prerelease], [])  # may be blank
 # The platform version is "major.minor" only.
 # The full version is "major.minor.micro[-prerelease]".