Escape '+' in escape_string()

'+' needs to be escaped. Without it, my line with '+' in it was being appended every Chef run, infinitely growing the file.
Merge pull request #2 from jblaine/patch-2

Escape '+' in escape_string()
bumping to 0.2.6
fixing replace_or_add
bumping metadata
bumping metadata
removing debugging lines and bumping
removing debug lines
fixing append_if_no_line by removing Chef::Util::FileEdit completely
reformatting block
adding +, moving escapetring to libraries/default.rb
bumping version to 0.3.1
implementing resources without Chef::Util::FileEdit
bug fixes around new_resource.path
adding TempFile
replace_or_add seems to be behaving
preserving file owner and permissions in replace_or_add
updating provider implementations
bumping to 0.4.0
updating README