Comments for weave.jl script format

[cnrrobertson]

Weave.jl can use either a markdown (.jmd) or script (.jl) format. When using the script format, any comment line written as #' or #%% is considered a "document" line as seen here.

When writing document lines in the script format, it is very convenient to have #' automatically inserted after pressing enter or entering insert mode with 'o' instead of the usual #. This can be accomplished by changing the filetype comments option from:

setlocal comments=:#

to

setlocal comments=:#',:#%%,:#

in https://github.com/JuliaEditorSupport/julia-vim/blob/2bd1c7516ef15381cdc82c66cf214ccdb103ba31/ftplugin/julia.vim#L16.

If this seems like a reasonable addition, I'm happy to submit a PR. It's easy enough to do individually, but I thought it might be useful to the community as a whole.