Things to do in this branch:

add "kern#N" syntax to assert C^N continuity for a kernel that might have less continuity

bug fix: print in pthreads target should work (but we should also
  generate a warning about non-determinism)

print: print to stdout, instead of stderr; allow output to be directed to a file too

print: syntax of printed tensors should match language

dynamic-length sequences (done, except for smart memory management)

curl 2D and 3D (done, but 3D needs to be tested)

support iteration over image indices

Add a "snapshot" keyword to annotate strand state variables.

use a persistent pool of workers for the SMP version so that
start up costs are reduced.

add support for kernels with odd-support

change syntax for conditional expressions (use C syntax instead of python)

bug: allowing int on one side of conditional expression assigned to a real

better error messages for
  "printf" instead of "print"
  "float" instead of "real"

add "clerp" function that is the composition of clamp and lerp.

optimize away dead branches of conditionals as part of HighIL contraction
(maybe other contraction phases too).