Add "Analysis/Manipulating Data" docs section

[jeromekelleher]

Right now it's very hard to find the documentation for how to read and write data using the tables API. There's a whole bunch of different ways of doing things, but no examples to show you how to do them (at least in the tskit documentation itself).

I think we should add this section which gives short examples of the various different approaches, and discussing any performance implications.

We should think about how this overlaps with the tutorial content

Things to illustrate (in no particular order):

• Writing tables row-by-row
• Reading tables row-by-row
• Updating a specific row (noting efficiency implications for ragged columns)
• Reading a column
• Writing a column
• Pulling out a "subtable" with numpy indexing
• Subsetting a table in place
• Remapping IDs

[jeromekelleher]

We would also want to update the documentation for the relevant methods to link to the relevant examples, of course.

[jeromekelleher]

The accessing table data section should definitely get moved into this new section, and we should also think about how to section that "Tables and Table Collections" section better.