Added replace module

Heavily based on existing lineinfile module, but where it literally tests a regexp against
*each individual line* of a file, this replace module is more analogous to common uses of
a `sed` or `perl` match + replacement of all instances of a pattern anywhere in the file.

Was debating adding `all` boolean or `count` numeric options to control how many
replacements to make in the destfile (vs currently replacing all instances)

Noted use of MULTILINE mode in docs, per suggestion from @jarv