GitLab

Renamed the transform() method into the terser map(), which is
more in line with other reactive and functional programming
frameworks and languages, and added a filter() method as well.

Updated documentation with examples for each.

Bug: NONE
Test: cast_base_junit_tests, cast_shell_junit_tests
Change-Id: I45797698500d829f175e1b350abe71185c03ff7f
Reviewed-on: https://chromium-review.googlesource.com/956970
Commit-Queue: Simeon Anfinrud <sanfin@chromium.org>
Reviewed-by: Luke Halliwell <halliwell@chromium.org>
Cr-Commit-Position: refs/heads/master@{#546186}