Rapidtide

* Fixed a critical bug that had been introduced in the last round of changes to findmaxlag.
* Disabled numba for findmaxlag (it seems to cause problems for some users).
* New option --skipsighistfit to omit fitting a Johnson SB function to the significance histogram.
* Fixed the usage statement.
* Fixed a bug that set ampthresh to zero when not doing significance estimation.

* Fixed a bug that made it impossible to specify --regressortstep.
* Added undocumented option --nonumba to turn off just in time compilation if there's a problem with it.
* Print rapidtide version on launch.
* Made pandas import explicit (sklearn requires it).

* Some fixes to usage output.
* Added functions for fitting trapezoids (for risetime calculations).
* Changed argument parsing and option output to avoid conflicts
* Added an option to not zero out bad fits (so as not to skew lag statistics)
* Improved fitting of probability distributions.
* Better handling of failed correlation peak fits.
* Now installations should work properly if not installed using git (fixed _gittag import problem).

* Added a tool (rapidtide2std) to register all output maps to MNI152 coordinates (requires FSL).
* Made a 3mm resolution ASPECTS map for use in tidepool.
* Reference data is now properly installed, and tidepool can find it reliably.
* Redid the version information. Rapidtide now records both the release version and
the git hash in in the output data to help with data provenance.
* Reorganized the distribution into what seems to be a more canonical layout.
* Resolved the issues I seem to have introduced with Python 3 compatibility.
* Significantly cleaned up resampling and filtering code and improved reliability.
* Added some unit tests for critical routines. Strangely, they all fail on Travis-CI,
but work on my local machine. It seems to be a numerical precision issue. The answers
are rightish, just not right on Travis.

* Some bug fixes in filtering and resampling code.
* Beginning to add automated tests.
* Biphasic mode is now fully implemented, including two-tailed significance calculation.

* First release