fix directory names in README
Allow overrides definitions using strings instead of symbols
Fix failing spec; Update location of Chef’s GPG key.
Merge pull request #405 from dwradcliffe/patch-1

fix directory names in README
Merge pull request #406 from servebox/software-as-string

Allow overrides definitions using strings instead of symbols
[DEB] Replace invalid characters with underscores

The previous replacement character, dashes, hold special significance in 
the Debian package spec.
[DEB] replace dashes (-) to tildes (~) in version

Dashes hold special significance in the Debian package versions. Versions
that contain a dash and should be considered an earlier version (e.g.
pre-releases) may actually be ordered as later (e.g. 12.0.0-rc.6 >
12.0.0). We'll work around this by replacing dashes with tildes.

Fixes #396