Resolve "More information than just "Unable to create plot.""

Closes #10

See merge request !5

Ensure value range isn't 0.0 #20

Closes #20

See merge request !11

Convert from optparse to argparse #15

See merge request !8

Resolve "RuntimeWarning with stats when stddev==0.0"

Closes #19

See merge request !10

Force the range to be -0.1 through 0.1. This is what matplotlib does
anyway, and this suppresses a warning.

Slightly simpler, smaller, and easier to style. As a bonus, you can
copy/paste them.

adding extra checks when variable data is loaded to prevent crashing and some cosmetic changes to html report output

added global and variable attributes to report pages; fixed bug in the io module that was causing global attributes to never be loaded; corrected the behavior for purple marking circles behind small numbers of mismatch points and added that behavior to some other kinds of mismatch plots

fixing variable sync in the gui and making a preliminary change to improve statistic display precision

Raise built-in open exceptions if file inaccessible

Keep going if reportGen encounters a string variable

Smart GUI variable selection

If we had a file open in that "slot" (A or B) already, and the selected variable name is also present in the new file, pick that.
If that doesn't work, check to see if the selected variable name in the other file (B or A) is present, and if so pick that.
Otherwise stick with the existing default: the first item.

This should speed things up a little bit when bouncing between files, as the variable the user is most likely interested will already be selected.

In the GUI, if the user changes the A variable, and the A and B variables were the same, try to change the B variable to match.

Changed from catching activated to currentIndexChanged, as the former doesn't work when the selection is programmatically changed.