Fixes #708

Bump SBT to 1.0.4 and update plugins
Update Scala versions and sbt commands in .travis.yml
Replace run-main with runMain

Remove wires, replacing them with nodes

Make the check script allow different designs
Add FPU, ICache, and RocketCore to regress and use instead of Rob for CI
equivalence check

This transform replaces all wires with nodes in a legal, flow-forward
order

Move pad to object ConstantPropagation so other transforms can use it

* add graph node classes

* add graph representation usage pass

* remove pass using graph nodes so that firrtl can compile

* move google graph ir nodes to altIR package

Also let Travis know that equivalence checks can take a while

Add Yosys formal equivalence checking to Travis regressions

Also add Travis test for running this script on PRs

Defined as the range from ' ' to '~' [0x20, 0x7e]

This prevents collisions for one prefix (including temp) from
incrementing the suffix for other prefixes. Makes names more stable.

Refactor StringLit to use String instead of Array[Byte]

When calling verilator in a subdirectory like ./test_run_dir/...
verilator will read the verilog file from the current working directory
if there is a file there with the right name.  This fix specifies
the specific path of the verilog file intended.

not exit when --help is included in program flags

Adds programArgs to commonOptions
programArgs is all arguments on command line with out leading -/+
or are not bound to a flag.
Create simple test

* Update sbt to 0.13.16; add Scala 2.12 support.
To clean, test, and build Scala 2.11 and Scala 2.12 versions:
  % sbt +clean +test +publishLocal

* Update Travis to test in 2.11.11 and 2.12.3

* Try different way of providing Travis Scala version

* Attempt to get verilator built before tests.

* Make pathsInDAG walk all possible paths

Signed-off-by: Schuyler Eldridge <schuyler.eldridge@ibm.com>

* Use linearization order when finding all paths in DAG

Since InstanceGraph now has all modules in its graph, test ConstProp on all modules as a default behaviour.

- Need to think about how to target ConstProp only for a specific module?

Close #644