* small clarification of verbose flag

* nfischer's documentation suggestion

* verbose flag documentation in source file

* Use process.platform across codebase

* Use process.platform in tests

* rm -rf on a symlink to a dir deletes contents

* Fix comment typo

* Clarify comments

* Pass symlink directly to rmdirSync

* Skip rm -rf symlink test on windows

No change in logic.

This removes unnecessary imports of `common.js` in favor of the `shell`
package.

* cp: add error to not overwrite recently created files #631

* cp: add tests for errors not overwrite recently created files #631

* mv: show error when overwriting recently created file #631

* mv: add tests for error on recently created files #631

* mv: test remove unnecessary steps #631

* When glob.sync errors, return original array element

* Add test for cp with empty string

* Add common.buffer

* Fix comment

* fix(cat): do not cat directories

Fixes #707

* fix(head): do not let head() read directories

Also fixes a typo

* fix(sort): do not sort directories

Also fixes a typo

* fix(tail): do not let tail() read directories

Also fixes a typo

* fix(uniq): do not let uniq() read directories

We also had a test which called sort() instead of uniq(), so we never
actually tested the missing-file case. This fixes that as well.

This also throws an error for using a directory as output.

* fix(pipe): fix breakages with piped commands

* fix(mkdir): improve error handling around files

In particular, this fixes:

 - if we try to overwrite a file with a mkdir
 - if we try to create a subdirectory of a file
 - adds `continue: true` in spots where we missed it

Fixes #720

* Fixing tests on Windows