Added Email::attach_cid() returning CID
styleguided
Further changes related to PR #2807
attach files by absolute url
documentation repairs
Finally get rid of the CI_Router::_set_overrides() calls
Merge pull request #2808 from melounek/filename_as_url

attach files by absolute url
CI_URI changes related to the 'permitted_uri_chars' setting

 - Initialize and cache the value in the class constructor instead of searching for it every time
 - Removed the preg_quote() call from _filter_uri() to allow more fine-tuning from configuration
 - Renamed _filter_uri() to filter_uri() - it was public anyway and using it cannot break anything

Related: issue #2799
Fix #2822: Incorrect usage of fwrite()

We only used to check (and not always) if the return value of fwrite() is boolean FALSE,
while it is possible that the otherwise returned bytecount is less than the length of
data that we're trying to write. This allowed incomplete writes over network streams
and possibly a few other edge cases.
Fix #2799 by adding conditional PCRE UTF-8 support to CI_URI::filter_uri()

Also did a tiny micro-optimization in the Utf8 class.