Allow setting a common config file for all lolcommit repos

[matthutchinson]

Achieved via a new ENV variable (quick to implement) OR..

Perhaps create a new file with --config --global to exist in ~/.lolcommits/config OR this file is created on plugin being enabled in the first repo. If we go with this approach, there are 2 options for knowing working out the settings to apply;

• Config settings hash in the repo dir ~/.lolcommits/{repo}/config contain all settings for that repo, if no config file exists, the global config is applied.
• Partial (or full) config settings hash in the repo dir ~/.lolcommits/{repo}/config contain all settings for that repo that then get merged with the global config hash.

Requested in #305

[matthutchinson]

Also requested in #297

[theapache64]

Any update on this?