Support write all type of forcings in ```write_forcing``` function

[xldeltares]

Write_forcings does not yet support complete writing of boundary, meteo and laterals, needs improvement. Propose to write forcing file as per forcing type, e.g. 1d boundary, 2d boundary, 1d lateral, 2d lateral, 2d meteo then write one ext file. Note ext file will validate file path, which does not seem to work with relative path. therefore a temporart soluton of reset work dir could be used.

[xldeltares]

This also applies to read_forcing

[xldeltares]

FIxed with write_ext function