Reworked stencil access syntax

- Removed stencil expression syntax ($ ... $ is now implicit)
- A stencil access is now u[[i, j]].
- Added notes on progress for cartesian branch
Merge branch 'master' into cartesian
Added helpful error message
 Also added build to gitignore
Added safety checks for stencil indexing
 Also updated slightly printout
First example that produces something "close" to working
 Also added error messages
Made new stencil access syntax, i.e., u(i, j) instead of u[[i, j]]. Does
not work yet
 The current version does not get function definition scopes correct,
because I have removed the rule from the parser (otherwise I got a
shift/reduce conflict). The best approach to solve this might be to have
a meta-node which handles all function call-like
Should reproduce existing (non-stencil) compilations
 Not checked, and stencils do not work yet
Compiling stencils now works
 However, not all of the error checking appears to work. Need to
investigate a bit further.
Appears to work well with stencils
Implemented implicit declaration of stencil variables
Creating / adapting runtime interface for Cartesian equelle programs
Uncommented more tests for cartesian
Added Stencil motifier
Added entity sets to execute a stencil
First version of stencils supported in compiler
 Solves the heat equation explicitly.
Fixed bug in heat equation discretization
Merge branch 'master' into cartesian

Conflicts:
	compiler/ASTNodes.hpp
Merge pull request #26 from sintefmath/cartesian

Cartesian
Move misplaced files and fix prototypes.
Merge pull request #28 from atgeirr/fix-cartesian

Move misplaced files and fix prototypes.