Add logdistance to list of extrinsic parameter names for ensemble and differential evolution steps
glue.ligolw:  add unit test for tokenizer module

- update doc strings so that doctest passes, and run doctest in unit tests
glue.ligolw:  update table's docstrings so that doctest passes

- enable doctest of glue.ligolw.table module as unit test
glue.ligolw.table:  use super() to chain to parent classes
glue.ligolw.table:  use classmethod as a decorator
rate.py: performance improvement

- import bisect_right() symbol into our namespace to avoid external module
  symbol look-ups inside inner loops
rate.py: use more accurate expressions for LinearBin's .upper() etc.

- and .lower() and .centres()
- add examples to documentation to serve as tests
glue.ligolw: remove the DefaultLIGOLWContentHandler mechanism
glue.ligolw: remove dbtables.DBTable.connection class attribute