added syntax section to design doc

The design document `language/design` now has a "Syntax" section that will list
all syntax rules and describe them in detail. This is a good opportunity to
flesh out the syntax and style of the language, and get an overview of what is
already implemented.
removed index of listings
added block_expr doc

Tweaked the func_expr syntax description in the design document. Also added the
block_expr section that describes fairly convoluted block expressions.
tweaked design doc layout
added syntax for literals and primary_expr

Extended the design document with specification of literals and primary
expressions. Very clean.
fixed typos
trying to get LaTeX to format grammar

Actually as it turns out, LaTeX does an absolutely horrible job of laying out
text. The design document is horribly disgusting, with headings stuck to their
preceding paragraph, orphans and widow paragraphs, you name it. I have
absolutely no idea how this bullshit comes about, as LaTeX is supposed to be
very good at these things. But even a remotely challening layout, such as a few
lstlistings on a page, completely break the layout. You can actually see the
headings moving closer to the previous paragraph as a page progresses, as if the
layout engine had no clue at all what to do. Damn.
using verbatim for grammar and samples

This resolves a lot of the issues that lstlistings introduces in the layout of
the text. Maybe it's time to write a replacement?
added grammar to design doc

Added ifcase_expr and tuple_expr to design document
Merge branch 'master' of github.com:fabianschuiki/Maxwell