Investigate suggestions for SLFhelper

[Jennit07]

At the SLF information session, a suggestion was to have LTC variables easily accessible for doing selections on. Investigate how we can allow SLF helper to include all of the LTC variables during the column selection without always having to specify a list.

[Jennit07]

When i looked into this, i found that you can already do this by using the following code:

read_slf_episode("1920", col_select = ltc_vars)

I think this would be the case of updating the main page on github to show this as an example so that analysts can use this