- tests currently fail

 -to later allow for CUDA implementation
 -some optional-import acrobatics
  to fail gracefully if a module (especially CUDA)
  is not available
 -as of this commit, nothing beyond lal implemented yet

 -first search should be standard non-transient GridSearch for comparison

Previously, this functionality was part of GridSearch, this splits this
into a separate subclass to ease future development.

 -"AttributeError: 'function' object has no attribute 'gridcorner'"

 -new output: full (t0,tau) Fstat map,
  if bands in those params are searched
 -one file per Doppler grid point

Closes #9

Previously, a check was done to ensure that all initial positions of the
walkers would yield a non -np.inf prior. This extends this to also check
the likelihood evaluations. The method is also simplified partially

Partially resolves issues in #6

The variable name was misleading and hence renamed

This renames the input sftfilepath to sftfilepattern and adds
documentation on how that should be used, i.e. a colon separated list of
wildstring or exact matches. In globbing for all matches, the colon
split is added in. sftfilepath is still used by `Writer` since
an exact path is known.

A search, based on Reinhard's J0537-6910 work, in which the search is
performed over F0 in a sliding window. Able to track changes in the
power and frequency of the signal.