Filter: preserve previous error if func succeeds

Report ExecForEach command exit errors to the pipe

short-circuit on error (fixes bitfield#141)

Tweaks

Merge pull request bitfield#139 from bitfield/http

Add HTTP support via Do, Get, Post

Change some t.Errors to t.Fatals

Don't close pipe in SetError (bitfield#120)

Fixes bitfield#117.

* The pipe shouldn't be closed on SetError function

* Fix TestExecRunsGoWithNoArgsAndGetsUsageMessagePlusErrorExitStatus2 test. It was not checking that exit status is two

* Update test name to match what is really doing

* Fix example for getting exit status from exec

* Add new example for exit status not zero on Exec

Merge pull request bitfield#106 from bitfield/jq

Add JQ filter

Merge pull request bitfield#101 from bitfield/filter

Make pipe filters concurrent

Co-authored-by: Puchen Xu <korolxu@umich.edu>
Co-authored-by: Christoph Petrausch <263448+hikhvar@users.noreply.github.com>

Fix some test failures on Windows

Co-authored-by: Aaron Huntley <aaron.huntley2007@gmail.com>
Co-authored-by: Brian Hasden <bhasden@gmail.com>
Co-authored-by: Umang Vanjara <umang.vanjara@gmail.com>