Change way upper limit prior is computed slightly.

* Upper limit prior is based on width of upper-lower, not just
  upper value.
* Doc fixes.
Add initial version of filter response code (response.py).

* Code imports but has not been tested.
* The use of this code has also not been implemented in the fits.
* Bump version number to 0.1.4
* Fix subdir name in .gitignore
Debug filter integration code.

* Filter integration code now passes by-hand tests.
* Added support for delta function responses.
* Added new normalization options: none, flat.
* Filter integration still not implemented into fits.
Added support for response functions to fits.

* Added response function control to mbb_fit, run_mbb_emcee,
  and likelihood.
* Changed the way responsedir works so it is also the location
  of the specification file for response.py
* Added ability to specify boxcar and gaussian filters.
* Change the way that the parameters of a delta function response
  are handled.
* Added capability to have photon counting devices in response.
* Added normal blackbody class to modified_blackbody
Bump version number, change gaussian filter sampling.

* Version number bumped to 0.2.0, since filter integration
  is a significant feature.
* Change Gaussian filter sampling to FWHM/7 rather than FWHM/11
Bug fixes to get filter code running.

* Fix various minor bugs in making filter code run.
* Set module version number, use that in run_mbb_emcee.
  Unfortunately, I don't see how to set that up in setup
  automatically.