add support for processing copy/directory file contents.
process content before engine for even more flexibility.
Consistent case for overwrite answers
Merge pull request #290 from stephenplusplus/async-error

Error can be passed into async() + new helper method.
Merge pull request #280 from ctalkington/copyProcess

add support for processing copy/directory file contents via function.
fixes #294 - bind `this` to `runInstall`.
check for updates.