Add centralized logging to the RubyGit gem

[jcouball]

Description

As a user of the RubyGit gem
I want to be able to see what git commands are executed as I use the RubyGit gem
So that I can debug my use of the RubyGit gem

Add a centralized logger as an attribute to the RubyGit module.

Using the logger:

RubyGit.logger.debug('Debug message')

Setting the logger to capture log messages in an instance of StringIO:

require 'logger'
require 'stringio'
log_device = StringIO.new
RubyGit.logger = Logger.new(log_device, level: Logger::DEBUG)
RubyGit.logger.debug('Debug message')
log_device.string.include?('Debug message')
 => true

By default, RubyGit.logger should be an instance of NullLogger.

What is changed?

ruby_git.gemspec

• Add runtime dependency on 'null-logger'

lib/ruby_git.rb and lib/ruby_git_spec.rb

• Add the module attribute logger which defaults to an instance of NullLogger.
• Change how RubyGit.git is documented so it shows up as a "Class Attribute" in the yard documentation to match how RubyGit.logger is documented.

lib/ruby_git/worktree.rb and lib/ruby_git/worktree_spec_initialize

• Log creation of Worktree instances at debug level.

What else was changed and why?

• Nothing

[frankthrock]

Looks good!