parallelize process_each
update to elixir 1.0
Update Earmark for footnote support
Support passing Earmark.Options
Markdown.render has default %Earmark.Options{}
Cleanup TacoSmith module

1. don't import Enum

2. process_each becomes process, old process goes away

3. process prefers a predicate filter function, but has a clause that accepts
regexes and constructs the predicate function
use my earmark for now
Support for YAML metadata in sidecar files

Personally I prefer this to inlining them at the top of markdown files, but
this method of metadata support also has the advantage of lending metadata to
files that you otherwise can't inline them in.
readme updates