Add different file formats

[evanthegrayt]

It'd be cool if this gem knew how to read/write yaml files. The only thing that would need to be added is new load/write methods.

This will actually help with another design problem I'm having. I want to add a to_md method at the entry level that will return the entry as an array of markdown lines. We already have to_json and to_h, at the entry level, so to_md would be nice. Then, when writing a file, we could just do

File.open(file, 'w') do |f|
  entry_list.each { |e| f.puts(e.to_md) }
end

The only thing I don't like about this, is I don't feel like the config for markdown should be in the Entry class. In other words, this feels wrong:

StandupMD.configure do |s|
  s.entry.header_depth = 2
  s.entry.bullet_character = '*'
end

BUT, if we have different parsers for YAML, Markdown, etc, then the config can live in those classes.