Decrease model tests precision.
Merge pull request #259 from francisco-dlp/decrease_model_tests_precision

Decrease model tests precision.
Remove debugging print
Ignore Thumbs.db (windows meta-data file)
Fix ValueError on remove_background()
When selecting a range by remove_background(), a ValueError is
raised initially when the left value is assigned, and the right value is
yet to be assigned (since the left can be higher than the right value).
Avoided by:
1) Setting default values to NaN, and not update line in plot until both right and left are set.
2) Checking which value is truly the left and right one before drawing line.
Small fix to remove_background() change
The span selector edges can no longer be reversed.
Update CHANGES.txt for 0.7 release.
Merge pull request #262 from francisco-dlp/update_changes

Update CHANGES.txt for 0.7 release.
Moved range selector left-right switch to widget

Previously suggested switching left and right in
BackgroundRemoval.bg_to_plot(). Here changed to doing it in
ModifiableSpanSelector, by changing which edge is moved when crossing
over.
Made ModifiableSpanSelector edge switch strict

Fixed imprecision in edge switch in ModifiableSpanSelector when the
change in position was large, i.e. it now precisely keeps the position
of the edge being passed over.
Add docstring for the public subpackages.
Automatic style corrections courtesy of autopep8.
Merge pull request #263 from francisco-dlp/document_public_modules

Document public modules
Add DielectricFunction to set_signal_type docstring.
Merge pull request #264 from francisco-dlp/add_df_to_signal_type

Add DielectricFunction to set_signal_type docstring.
RENAME: Signal.apply_function -> map
Automatic style corrections courtesy of autopep8.
Add notes section to map docstring to explain the differences with the Python function.
Merge pull request #265 from francisco-dlp/RENAME_apply_function_map

Rename apply function map