Merge pull request #15 from plinss/master

Get default date from input file modified time
Ugh, another case where I need to consider 'dfn' a dfnType.
lowercase link texts when pulling anchor data. fix possibility of empty linking texts.
Get it right this time.
Make propdef/descdef parsing fail with a fatal error, not a crash.
Refactor propdef/descdef handling to ensure canonical key ordering, and flag individual missing lines.
Replace plain apos with curly quotes when it looks like a possessive or a contraction.
Add auto-genned ids to all issues in the spec. These are stable against changes outside the issue, but shift if you change the issue.
Move header self-links to a separate function, add issue self-links.
Make heading functions only run on headers that haven't been processed yet.
Warn for headings that don't have an explicit id.
Make bikeshed generate self-links for examples and notes too, if they have an id.
Hell, let's catch <li> and <dt> too while we're at it.
Whoops, md5 expects a bytestring.
Make the ref manager recognize curly quotes when finding alternates for text.
Propdef parsing needs to strip the whitespace from its values. Descdef already did this for some reason?
Allow partial propdefs and descdefs.
Update the docs about partial propdef/descdef.
Update docs regarding issue id generation.
Update docs regarding self-links.