Add new function that reads Geosoft grids.

Upload test grd file
fix ValueError: cannot convert float NaN to integer with datetype (int)

These variables usually don't have any meaningful information and they
are usually not being converted to Unicode characters properly, what
makes difficult to save the dataarray as a netcdf file. I think it's
better to ignore it for now unless we have a good reason to include
them.

Add a netcdf file that hosts the expected grid.

This way we avoid having to install netcdf4 for testing

Upload order = -1 and test

Update compressed grd file

Define a global variable VALID_ELEMENT_SIZES for the valid values that
the ES variable can take. Compare n_bytes_per_element against ints after
shifting its value if its greater than 1024 (compressed grid).

Move the snippet that decompresses the grid into its own function. Avoid
creating numpy arrays that hold a single element for the variables in
the additional header.

The previous refactor didn't worked with compressed grids with multiple
blocks. Restored the compressed_blocK_sizes and block_offsets as arrays
and fixed the for loop.

Flake8 complains with leaving a space before a color, what makes sense
for colons that go after a statement (function definition, for loop, if,
etc). But it complains about the spaces before a colon used in slicing.
Black already handles the first case, so it makes sense to ignore E203.

Remove all the sample grids that weren't being used in the test suite.

… grd-oasis-montaj

Use proper sin function and fix the sign of the coefficients in the
rotation matrix.

Co-authored with @mdtanker