Tweak gh_releases

[JedMeister]

Change gh_release default behaviour to only show latest stable by default, also removing pre-release versions (assuming that they contain alpha|beta|rc keywords) from the output. Previous behaviour can still be obtained via gh_release --all --pre-release <user>/<repo>:

Usage: gh_releases [OPTIONS] <user>/<repo>

Options:
    -h|--help   show this help and exit
    -a|--all    show all (stable) versions, not just the most recent
    -p|--pre-release
                include alpha, beta and rc versions

Env Vars:
    # used for github api
    GITHUB_USER
    GITHUB_USER_TOKEN

    # retain temp files and set x
    DEBUG

    # omit tags or releases in output respectively if set
    NO_TAGS
    NO_RELEASES

Note: Setting GITHUB_USER and GITHUB_USER_TOKEN environment variables are
      recommended. If not set, multipage results may be unreliable.