Issue/198 inconsistent search replace

[sanderr]

Fixed bug in bumpversion.util.contains that leads to incorrect matching for multiline searches

closes #198

I believe there is currently still one inconsistency remaining where bumpversion would not work if either the config or the version file has CRLF line encodings. I did not test this (it's just an assumption based on reading the code), nor did I make any changes to this behavior.

~~(If accepted, might I ask to add the hacktoberfest-accepted label to the pull request? I mean to follow through on this either way of course.)~~

[sanderr]

Looks like the line endings issue is already known: #223.