Fix 'asiddha' to run to convergence
Fix bug in asiddha-lopa

We should match against 's' and 'k', not 's' and 'ku'.
Add basic Dhatupatha

Data comes from [1], with some alterations.

[1] http://sanskritdocuments.org/doc_z_misc_major_works/dhatupatha_svara.itx
Add dhatupatha.py
Add more tests
Add 1.2.4
Add tests for classes.py

Along with some other miscellaneous changes, which will be fleshed out
in future commits.
Add memoization for 'Sounds' and 'Pratyahara'
Add support for 'BavAmi', 'Bavanti' etc.

In addition, start converting the test files to a format that isn't
quite so redundant.
Add sandhi for 'n' retroflexion
Add support for e.g. 'krIRate'

In addition, start refactoring some more code. Using decorators to mark
valid rule functions seems a lot tidier than updating a master list in
ashtadhyayi.py, and moreover it should make it easier to show rule
traces in the future.
Add a variety of new test cases

TODO: make all of them pass!
Add tests for vibhakti.py
Fix IndexError problems with empty Pratyaya
Remove extraneous test code
Add support for 'na-lopa' in staBnAti etc.

This causes other seemingly unrelated tests to fail. These will be
addressed in a future commit.
Add support for e.g. 'jAnAti'
Add support for e.g. 'jAnIte'

In other words, add atmanepada support for 'jJA'
Move rule decorator code to decorators.py
Fix 'it' letter added by 1.2.4

This should be 'N', not 'k'.