Bar charts enhancements

[clayrat]

Supersedes #161, fixes #214 and #223.

This PR contains:

• A fix for incorrect logscale axis label rendering
• Customized labels on individual bars (based on Add data point labels #161)
• Ability to use a logscale axis with bar charts
• Ability to render horizontal bar charts
• Ability to have internal ticks on an indexed axis (e.g., to render grids)
• Various linter fixes
• A test demonstraring horizontal logscale bar with custom labels and an index grid

[clayrat]

Here's the output of the new test demonstrating added functionality:

[clayrat]

@timbod7 @bravit what do you think?

[timbod7]

Oh - dear. I just took a look at #161, and see that it ended in me saying I'd take a look in a few days. in 2017!

[timbod7]

A great set of changes. Thank you!