Add a read_csv method

[DocOtak]

This PR hacks the read_exchange apart a bit an reuses most of the machinery to allow for a more generic read_csv method with the following rules:

• No comment header or anything above the label line (no comments, no stamp, no nothing)
• Params and unit labels must be a single line, with units in square brackets if present. e.g. `EXPOCODE,STNNBR,[...],CTDPRS [DBARS],
• The normal exchange rules for the data block apply.
• No END_DATA the data should just end.

It should be possible to read concatenated CTD data as long as the above rules are followed and it kinda looks like a bottle file. I haven't tried this though.

[DocOtak]

This wasn't... clean, need to try reopening the PR