Support for block comments

[colemand77]

Seems that syntax highlighting for block comments

comment
some comments
go here
end comment

is not supported?

This is the block comment format described in the ledger documentation

I apologize I don't know Vimscript - I'd just submit a pull request for the feature if I did.
If I can reason it out I'll submit one.

[alerque]

Support for block comments was added thanks to @rohieb in dbbfbc1 and merged as part of #63.