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
revive a non-functioning test
tested on Windows
Remove undocumented Record.new(tuple) feature
Improve docs for Enum.all?/2, closes #1508
Dont escape " in shell commands on windows
Merge pull request #1510 from ericmj/mix-cmd-win

Dont escape " in shell commands on windows
Merge pull request #1507 from AtKaaZ/reborntest1

revive a non-functioning test
Merge pull request #1511 from guilleiguaran/with_index

Move definition of with_index below
Add Enum.reduce/2 that sets initial value of acc to the first element of collection