Move clap configuration to cli.yml

[donniebishop]

Was reading through the clap documentation and saw this feature to move the clap configuration out into a .yaml file. Cleans up main.rs a little bit, and the yaml file has a nice syntax for adding any new options or subcommands.

Recompiled arch-audit and tested that usage and behaviour of the binary seems to be unaffected by this change:

debug $ pwd
/home/dbishop/projects/arch-audit/target/debug
debug $ ./arch-audit -h
arch-audit 0.1.4

USAGE:
    arch-audit [FLAGS] [OPTIONS]

FLAGS:
    -h, --help          Prints help information
    -q, --quiet         Show only vulnerable package names and their versions
    -u, --upgradable    Show only packages that have already been fixed
    -V, --version       Prints version information

OPTIONS:
    -b, --dbpath <dbpath>    Set an alternate database location
    -f, --format <format>    Specify a format to control the output. Placeholders are %n (pkgname) and %c (CVEs)
debug $ ./arch-audit -q
libtiff
bzip2
jasper
libwmf
debug $ ./arch-audit -V
arch-audit 0.1.4

Hope this is of some help or use. Let me know if there's anything else I should do before this can be merged.

Note: Resubmitting due to fudging the first PR up