Add support for multline

[notjagan]

This is simply an intermediate pull request for before #46 is merged. I do not expect this to pass the checks because it will once this is merged in and the other request is merged in since the other request fixes the checks itself.

[physikerwelt]

@notjagan Why don't you focus on getting #46 straight first?

[physikerwelt]

please rebase

[HowardCohl]

@notjagan Have you rebased yet?

[notjagan]

@physikerwelt I have now merged the branch to reflect the changes made in #46 and updated the code to work with pegJS 0.10.0. If/when this gets merged in, I will then create a pull request to similarly add \begin{split}.

[HowardCohl]

@physikerwelt If there is nothing wrong with this pull request, could you merge it please.

[physikerwelt]

what is the difference in the functions for multine and matrix. Can't you just create one functaion and assign it to both keys MATRIX and MULTILINE

[physikerwelt]

@HowardCohl what is the difference between {multline} and {align} beside http://tex.stackexchange.com/questions/239252/what-is-the-difference-between-split-multline-align-breqn-for-breakin. For each language construct we add into astutil we need to implement special visitor in other tools that base on texvc such as texer or texvcinfo https://github.com/physikerwelt/texvcinfo/blob/master/lib/extractors/subscripts.js#L77-L153

@notjagan can you take a moment to investigate parser.pegjs and figure out if there is a simpler way to support {multiline} in the same way as {align} is supported at the moment. And could you also make a seperate pull request for the starred commands. I think we should consistently support starts for all environments that have the star option.

[physikerwelt]

is this ready to be merged?