v0.2

Make it easier to use custom hgt tiles from a user-defined directory:

• New contour line settings template contour1_custom in map_targets.py.
• Custom hgt file directory defined by custom_hgt_dir.
• To improve speed, only tiles in the relevant area are passed to pyhgtmap.

Other changes:

• Adjust some map targets to use custom hgt tiles.
• Small addition to reduce_data.py: deleted unnecessary linestring relations.
• Update Readme.