Better error messages

[kvelleby]

This PR improves error messaging at crucial points in PRIOGRID. It also updates missing documentation and fixes some bugs:

• speibase files needed local subdirectories to be created, but this was not currently done.
• linight url only worked from browser. found the urls through an api, and also updated the data to v10.
• the config parameter was missing from documentation in most functions
• the checksum approach was not written out, now there is a plan for checksums.