Combinator builtins

[dag]

For example, code like this is perfectly valid:

false
or begin
    ...
end

However currently if you type this the third line will not be automatically indented, and if you use endwise the end will actually be dedented one level more than the or begin!

To solve this we need a list of all these "combinator" builtins (only builtins have this power), and also remember that they can be chained, for example if not begin. Also, the b option should perhaps be removed from some or all of the UltiSnips snippets.