Add gcc task

Initial step toward add common compiler wrappers
Ignore `bin` instead of `build`
Combine build modules

By combining these modules we can reduce code duplication and centralize
the "run in" code to one spot
Add common compiler wrappers

Add wrappers around gcc/g++ and javac so that they can be invoked from
inside xnt
Ignore docs/build directory
Update documentation for new xnt.build.cc module

Move notes/documentation about build wrappers to new page and add
documentation for new "Compiler Collection" module
Modify modeline
Update README

Update pip install: add optional 2

Update example build.py: fix build import and call

Update Usage: rename `help` target to correct `list-targets`
Remove gcc task for it is now in xnt.build.cc
Add tests for compilercollection (cc) module
Add initial hack for `-D` parameter passing

This allows for invocations of Xnt to accept arguments of the form
`-D{name}={value}` to be inserted into the build.py's `properties`
dictionary. Currently, it's only over writing the dictionary; I
intend to clean this up and have it only over write the specified
key(s)
Update test to potentially better test
Update Param Passing to not override existing

When passing parameters to build, xenant should only override the
parameters being passed; not the entire dictionary
Update documentation: Add Parameter passing

Restructure documentation to better suite the parameter passing
section(s); add two sections: how to invoke xnt to pass parameters,
and how to add/use them in the build file
Merge branch 'refactor_build_modules'

Conflicts:
	.gitignore
Merge branch 'addParamPassing'

Conflicts:
	docs/source/buildfile.rst
Increment Version. Update Release Notes