Incremental update

What's Changed

The major additions are:

• color interpolations and new scales to support interpolated colors, including facilities to interpolate within the LCH color space.
• basic histogram and binning support
• initial setup for Date oriented scales and relevant date "ticks" and logic for associated 'nice' values.

• Generating images for DocC documentation by @heckj in #33
• Documentation updates by @heckj in #45
• Updating and fixing CI build issues by @heckj in #37
• LCH cleanup by @heckj in #38
• External cli by @heckj in #39
• Closure interpolator by @heckj in #40
• Color updates and tables displaying them by @heckj in #41
• Binning by @heckj in #42
• Updates to tick methods by @heckj in #46
• Histogram tweaks by @heckj in #47
• Date scales by @heckj in #48
• tweaking date nice values logic and computations by @heckj in #50

Full Changelog: 0.7.0...0.7.5