Treat empty strings as generic for column type deduction, allow thousands separators

[pjkundert]

Allow missing (None) and empty ("") cells to be treated the same, for the purposes of deducing the column type.

This allows us to have empty cells (without the missingval), differentiated from missing cells (with the missingval), for columns generally containing numeric data, while retaining the correctly deduced column formatting.

Resolves #242

[eliegoudout]

I think you should split your PR in two:

• One for the SEPARATING_LINE fix
• One for your proposed modification.

Indeed, merging the fix should not be conditional to accepting/merging your proposed modification.

[pjkundert]

OK, removed SEPARATING_LINE fix.

Now, deals in deduction of int and float columns, and supports thousands-separators in ints, floats.