You can install this using in the usual Perl fashion:
perl Makefile.PL make make test # (or) env MQHOST="localhost" make test make install
If you checkout the github repo, you'll need to run the following commands git submodule init git submodule update
After this, you'll need to install Module::CAPIMaker and then Math::Int64.
Finally, you'll have to build the C API for Math::Int64:
perl ./Makefile.PL make
The documentation is in the module file. Once you install the file, you can read it with perldoc.
If you want to read it before you install it, you can use perldoc directly on the module file.