- Moves create_default_prior to the core prior file
- Makes fill_prior a class attribute
- Makes the BBH default priors its own file which is read in when
  figuring out the defaults
- Checks the example all still run

and time marg before moving onto dist and tiem nad phase marg

- Add doc file on CBC PE
- Add introduction text

Allows easier access to the Likelihood, GWT, WaveformGenerator, and
run_sampler

changed random seed to avoid multi-modal posteriors.  Added comments to tutorial so user can understand each step

Closes #68 by giving a simple interface to set the log-level (unless set
at the script level) and whether or not to use cached data.

Revert "Revert "Moritz Huebner: Removed default parameters for sampling frequency and time duration in the waveform generator""

This reverts commit 91e90f0d.

Revert "Moritz Huebner: Removed default parameters for sampling frequency and time duration in the waveform generator"

This reverts commit e4ac1430.

Moritz Huebner: Removed default parameters for sampling frequency and time duration in the waveform generator

If a label is given to setup_logger, the output is written to a file.

- This simplifies the way things are passed around
- Also fixes the spelling mistake of "interferometer" (my bad)

- Makes the plot_corner method an attribute of the result instance
- Removes the return of sampler from run_sampler
- Adds label and outdir to the result
- Fixes the GW150914 and BasicTutorial to run with the new interface