Support release versioning and snap builds

If the version consists of two components (package version and
release/build version), it is necessary to explicitly specify each when
building with fpm. This is particularly important for rpm packages...
otherwise a version string of "0.19.0-1.0.centos64" will end up as:

    Version     : 0.19.0_1.0.centos64
    Release     : 1

Instead of:

    Version     : 0.19.0
    Release     : 1.0.centos64

This patch also supports "snapshot" builds by default, which is just a
release version set to 0.1.$UTC_TIMESTAMP
Merge pull request #13 from mesosphere/release-ver-and-snap-builds

Support release versioning and snap builds