Add markdown insertLink and insertIMG functions
Create lightweight markdown editor from scratch

Code cleanup.

First pass at implementing @aron's mockups.

Fix bugs, breakout markdown into its own directive

Forgot to add markdown.coffee
Add checks to see if markup has already been inserted
Fix bugs by getting rid of a bad idea. Tighten up styles.
Add ngDoc documentation to markdown.coffee
Rebase to latest master, and implement some of Aron's suggestions.
Icomoon Cleanup. Delete unused icons.
Implemented more of Aron's suggestions.
Reorganized CSS, minor changes to documentation.
Rename things, fix embarassing spelling error.
Rename returnSelection() to userSelection(), remove unneeded parentheses, fix spelling error
Rename variables

Went with Aron's suggestion of suffixing raw nodes with 'El,' and got rid of the
variable 'ourIframeSelection' as it has nothing to do with iframes and the code
could be written without the need for that variable.

input -> inputEl
textarea -> input
Break out markdown styles into separate stylesheet
Remove $window dependency in markdown directive

Covert px values in markdown-editor.scss to use em. Note: I did this for all values except min-height on .markdown-preview which for some strange reason caused a weird flicker in Firefox.

Add 'markdown-' namespace to .preview and .preview-toggle classes.

Unnested CSS in markdown-editor.scss. Everything is well namespaced now so this is no longer necessary.

Apply consistent sentence case to the title attributes of the markdown tools.
Break up long lines of code over multiple lines
Merge pull request #1479 from hypothesis/markdown

Introduce zero-dependency Markdown Editor.