fixing a test to also work in Windows
used to do this:
'MIX_ENV' is not recognized as an internal or external command,
operable program or batch file.
Tested to work on both Windows and Linux.
However the following is seen on console:
Mix requires the compile path "ebin" to be inside a directory with the
 same name as the application name :no_mixfile,
got "s:/workspace.elixir.2013/elixir/lib/mix/tmp/Mix.CLITest/test env/ebin"

quick test with `make test_mix`
Merge pull request #1501 from AtKaaZ/mixenvWindows1

fixing a test to also work in Windows
Fixed docs typos and added  markers around functions in docs
Merge pull request #1502 from jwarwick/code_formatting

Fixed docs typos and added code markers around functions in docs
Improve docs for EEx.AssignsEngine, closes #1499
mix run now properly sets System.argv
Make it explicit that some tasks require a project to be defined
test_helper files still need to be required upfront

Since they have to be required upfront, it makes no sense to have
a Code.require_file("test_helper.exs", __DIR__) in Mix projects
since the files can't run in isolation anyway.
Fix some invalid error messages from Mix