Rename col to ctrl in code examples and tests

[nanxstats]

This PR follows #213 to rename col to ctrl (a more common abbreviation of "control") in code examples and unit tests.

[LittleBeannie]

Hi @nanxstats , can I ask a minor question before we merge? If we short control to ctrl, what shall we shorten experimental to? Shall we also shorten it into 4 letters for consistency with ctrl?

[nanxstats]

Hi @nanxstats , can I ask a minor question before we merge? If we short control to ctrl, what shall we shorten experimental to? Shall we also shorten it into 4 letters for consistency with ctrl?

I think exp is already the proper abbreviation for experimental.

It's really hard to find a 4 letter abbreviation for exprimental. However, it's not impossible to find a three letter abbreviation for control, if you are willing to use the (less common) ctr.

OR maybe you should just not abbreviate at all.