Version 1.1.0: transparent but for the letters

This is a release adds functionality for overlay tiles that have transparency (e.g. to add labels only) and includes a few bug fixes along the way.

New functionality:

• Map tile overlays (#114): see new section added to documentation for the feature. This feature was contributed by @jpn-- (thanks!)

Bug fixes:

• Documentation website bug fixed so side bar navigation is visible #168