Full rewrite begins: goal: API server and robust parsing

Copyrights of the existing codebase are transferred to Koodilehto Osk
Add basic support for downloading HTML documents

Features:

 * requires just the base governing body URL, which is then used to find
   all related meeting documents and agenda items

 * ability to set minimum HTTP request interval, 1 sec by default

 * ability to skip downloads if the page has been downloaded earlier,
   enabled by default

 * download.py included as an example
Add destination dir as an optional constructor argument to HTMLDownloader
Use logging from standard lib instead of just printing to stderr
Make download dirpath absolute to make log contents less ambiguous
Log download starts and ends
Pass the base url to the constructor
Strip the leading URL base path from the destination filepath

Example:

download_dir = "downloads"
url = "http://www3.jkl.fi/paatokset/karltk.htm"

Before this commit:
  => downloads/paatokset/karltk.htm
After this commit:
  => downloads/karltk.htm
Raise exception instead of just logging and returning None
Continue downloading if anything goes wrong with individual pages

The whole download process might be lengthy, so it's better to just keep
going and let the user know what went wrong so that she can come back to
it afterwards.
Rename agenda item -> issue page
Use Python 3

Reasons:

 - Klupu's parser code is written only for Python 3
 - the migration was really trivial since the codebase is still small
Add basic support parsing meeting documents

Parser code is heavily based on Klupu's parsing code.
Drop support for download_dir argument

Chdir before running is simpler
Fix datetime parsing to accept multiple datetimes
Add issue page parsing
Parse policymaker abbreviation from the meeting doc dirpath
Rename and refactor
Rename issue page -> agenda item
Remove unused logger from HTMLParser