replace form_data.signature by form.signature
foo.form_data() -> compute_form_data(foo)
make compatible with upstream UFL; need to optimize
remove one instance of compute_form_data; tidy up
Don't compute form data if we had kernels stashed on the form
Use form.signature rather than compute_form_signature
Merge pull request #327 from firedrakeproject/upstream-compatibility

* upstream-compatibility:
  Use form.signature rather than compute_form_signature
  Don't compute form data if we had kernels stashed on the form
  remove one instance of compute_form_data; tidy up
  make compatible with upstream UFL; need to optimize
  foo.form_data() -> compute_form_data(foo)
  replace form_data.signature by form.signature
Add extrusion documentation
Add introduction
Add kernel passing details
Add link to variational problems documentation
Add details on extruded mesh construction
Add Function Space documentation
move file
add preamble
fix off-by-one references
initial extruded function space rewrite
more extruded fspace doc
rearrangement
OPE doc introduction