Style: Misc doc changes

[kianmeng]

List of changes:

• Use common source url
• Add changelog to html doc
• Badges and more badges!
• Mix format module config
• Add changelog link to hex info page
• Always get latest ex_doc
• Set readme as default html page
• Add license section
• Fix code indentation and list numbering
• Fix markdown
• Use shorter package name
• Mix format code example

[kianmeng]

@mtchavez Any updates on this?

[mtchavez]

Thanks for the contribution. I addressed some of your suggestions and made a new release of v0.3.1.

[kianmeng]

@mtchavez Thanks! :+1: :tada: