New LCurve class to estimate regularization params

The new class behaves like any other solver but under the hood it runs
the L-curve and finds the corner value when fit() is called.
Too much precision in LCurve test

The test of the residuals mean and stddev had too many significant
digits
Still too much precision in LCurve test
SrTomo recipes use LCurve

Also switched the model to a square. This way they don't have to
download the tomo image all the time.
Merge branch 'master' into lcurve
Merge branch 'master' into lcurve
LCurve computes in parallel

Uses multiprocessing when given `jobs` argument.
Updated changelog with LCurve entry
Scaling in LCurve and opt out of loglog

Scaling before estimating the corner in LCurve for better identification
and added an option to not use a loglog scale.
Using LCurve in eqlayer recipes
Added docstring for LCurve
Filled in docstrings for LCurve

Also fixed some issues with doc formats.
Better ranges for lcurve in srtomo recipes
Merge pull request #90 from leouieda/lcurve

New LCurve class to estimate regularization parameters