Working on codegen

  Change name of MidIL Transform operator to PosToImgSpace.  Also added GradToWorldSpace operator to MidIL.

  Upated URL in header to diderot-language.cs.uchicago.edu

  fix comment

  Adding MidIL checking

  Better error messages

  Bug fix: add missing code to set CFG edges in destination

  Added checking for HighIL representation

  Working on checking

  More work on checking

  Working on IL checking

  Working on checking code

  Added more type info to HighIL operators to aid checking.

  Working on checking for HighIL

  Minor edits

  reorganize operators a bit

  fixed typo

  Slice support in HighIL

  Added types to pretty printing

  Added types to IL variables

  new files

  Moving IL types out of the Op structures into their own per-IL structures.

  Move MidIL types into their own module

  Started to work on IL checker

  Working on optimization and translation

  Added HighIL to MidIL translation phase

  Working on high to mid translation

  removed Transform from high IL

  Working on translation functor

  working on translation

  Adding new file for translation support

  Move test-kernel stuff to fields directory

  Added hash-cons representation of IL expressions

  Added assignToString function

  working on HighIL to MidIL translation

  Fixed header comment

Adding the files for the low-il specs

  Adding comments

  Implementing the census functor

  Working on debugging HighIL optimization

  Working on HighIL optimization

  Added some comments

  Tweaking MidIL definition

  Fixed bugs in mid-il and IL generator

  Working on HighIL to MidIL translation

  comments

  tweaking mid IL

  Added newProp and newFlag functions for nodes, stmts, and vars

  Made the IL generator more general to handle MidIL features

  Working on MidIL representation

  tweaking printing of SSA IL

  Moving high-IL stuff to its own directory

  Some work on SSA checking code

  Added BackwardDFAFn functor

  Added ForwardDFAFn functor

  New version of IL with translation to HighIL and pretty printing.

  Working on translation to HighIL

  Reorganize stuff to do with images, kernels, and fields into its own directory.

  Reorganizing source

  Added Var substructure to SSAFn

  Starting to add utility code for SSA representations

  Working on translation to HighIL

  Update

  Adding operations for fields

  Working on translation to IL

  Working on translation to IL

  Working on IL representation

  Add generator for IL operator structures.

  Working on translation

  Working on translation to HighIL

  Switch the translate code to take simple AST as its input type

  Working on translation to HighIL

  New file

  Adding equality tests and hashing support

  Added kernel printing code

  Debugging kernel support using test driver

  Added RawTypes module

  Starting to write a test driver for the kernel code

  Made kernel type abstract and added derivative cache.

  Working on IR

  Working on IL representation

  merge image-info directory into the IL directory

  Added normalize function

  Working on IL

  Parameterize the SSA representation over the operators

  Fixed syntax error

  New file

  Fix syntax errors

  Switched kernels to use rational coefficients and added definitions of common
  kernels.

  Moving compiler sources into src/compiler

  Adding file

  Some work on typing the basis

  comments and minor edits

  More work on type system

  More work on types; added well-formedness check

  Starting to work on internal-language representation of types.