Renaming the task to `psci` and writing the result of the command to the
`.psci` file.

Note that previous commits resolved #40

Note that this is part of the updates for PureScript 0.7, which along
with previous commits resolves #38

Migrating back to a stream implementation for the tasks to allow
conventient piping with other streams such as `gulp.dest`.

Merging stream refactoring for 0.7 updates.