Move TagInfo class to break import dependency cycle

Modules fail to import with a dependency cycle when using relative imports.
Use relative import syntax in existing packages

* Relative imports introduced in Python 2.5
* Should help distinguish local HTMLParser module from the one in the
  standard library

Inspired using “2to3”.
Use Pynche package’s __path__ to find data files
Fix up regex match checking; use simpler alternatives to regex

* str.replace(), str.startswith()
Make this “bkmk2<format>” script naming work, and document it
Move LICENSE file into src/ directory

LICENSE needs to be in the package directory to be accessible as a
“grail:LICENSE” URL.