This macro invokes a function which
returns an integer representing the version of the AST library
being used. The library version is formatted as a string such as
"2.0-7" which contains integers representing the "major version" (2),
the "minor version" (0) and the "release" (7). The integer returned
by this function combines all three integers together into a single
integer using the expresion:
(major version)*1E6 + (minor version)*1E3 + (release)