Add import Prelude.Functor in Prelude/Vect.idr

This is imported transitively through Prelude.List, but really should be
explicit.
Simplify Prelude.Vect.range
Better unification errors when name is out of scope
In particular, a unification problem which cannot be solved because it
uses a variable not in scope where the metavariable is bound.
Fixes #342
Merge pull request #424 from Melvar/correct-vect-instances

Add import Prelude.Functor in Prelude/Vect.idr
Merge pull request #425 from Melvar/simplify-range

Simplify Prelude.Vect.range
Add missing case for PEq to expandDo in DSL.hs
Temporarily remove java tests from .travis.yml
Because they don't work anyway. Will reinstate when the java build
isn't version number dependent, somehow.
Allow tests to be parallelized

Running `make -j16 test` now runs tests in batches of 16.  This takes 1m
(real) (6m user), whereas `make -j1 test` takes about 5 minutes (both
real and user).  There is a bit of funniness with cancelling `make -j16
test`; I get a bunch of directory/file not found errors.  I'm not sure
why.

I've changed the test printing format a bit; make, unlike, say, the
ninja buildsystem, interleaves outputs rather than buffering them.  I
chose to make sure that the perl script printed entire lines at one,
resulting in output like
```
Running test004...
Ran test004...success
Running test005...
Ran test005...success
Running test006...
Ran test006...success
Running test007...
```
rather than
```
Running test004...success
Running test005...success
Running test006...success
Running test007...
```
with the `success` appearing some time after the `Running testNNN...`
message.
Remove overlapped case in CodegenC
Update CHANGELOG
Update CONTRIBUTORS and CHANGELOG
Take CFLAGS from environment in Makefiles
Make .travis.yml repository-independent
Treat Int as unsigned in C codegen when zero-extending to Integer

This brings behavior into line with zext to fixed width integers and zext in the LLVM codegen, and ensures that cases where an Int wraps a size_t lose a minimum of information.
Change treatment of underscore in lambda
Treat as unnamed variables, rather than as patterns
Remove restriction on hole scoping
"it" now refers to the previous value at the REPL
Support signed integer comparison by introducing new primitives
Set java-rts version to a fixed working one and update shade plugin version dependency
Reactivate Java test, since new rts version is published