Handle code indenting

[smcguire-cmu]

Currently indenting needs to be done by the user, where each snipped must be correctly indented for where it is placed. This can lead to both confusion on the user forgetting what indent level the snippet they are writing is at, and the user needs to do their own indenting in the yaml file which is annoying and very hard to edit (manually adding spaces on each line). It also means a snippet cannot be used at different indents, e.g. if different branches of the tree lead to different indent levels.

It would be good to handle indents automatically, some kind of keeping track of the current indent level and adding it to the lines in the snippet inserted.