Tiledwebmaps

Large refactor of the library.

Added

- Added option for storing layout in ``layout.yaml`.
- Added scripts for bulk downloading imagery.
- Added ``min_zoom`` and ``max_zoom`` property to all tileloaders.

Changed

- Removed cosy1 dependency.
- Improved tile loading speed.

Changed

- Improved error handling and reporting.

Fixed

- Fixed bug that caused "Illegal instruction (core dumped)" on some devices. (Remove -march=native)