character_limiter now works correct for UTF-8 strings

strlen() doesn't return the actual length for unicode strings. For example strlen('سلام') returns 8, but length of سلام is 4. strlen(utf8_decode('سلام')) returns correct value 4.
Reference: http://www.php.net/manual/de/function.strlen.php#45407
removed newline from end of file
remove newline from end of file
count number of characters (with mb_strlen) instead of counting number of bytes with strlen
Merge remote-tracking branch 'asli/develop' into patch-1
Update the Session library docs

Signed-off-by: Michael <michael@webstart.bg>
Added class reference to the session docs

Signed-off-by: Michael <michael@webstart.bg>
refactored the class reference in session.rst to properly reflect the session class

Signed-off-by: Michael <michael@webstart.bg>
Merge pull request #2666 from xxaxxo/feature/user-guide-cleanup

Update the Session library docs
Removed extra from $name, since it does not follow the format of other form_ helpers. Form helpers use $extra as a string. On the form_input for example, the $extra is a string but placing extra in the first parameter results in an attribute on the resulting element called 'extra', whereas the drop down it does not. $extra is now passed along as works just as all other form_ methods do.
Update user_agents.php

Added Win 8.1 user agent to the array
Added post-increment for $count

It has been added the missing post-increment for variable $count.
[ci skip] Add/remove some newlines from the session docs
[ci skip] Update the Security class docs
[ci skip] Update the Parser library docs
[ci skip] Update the Pagination library docs
[ci skip] Update the Output library docs
[ci skip] Update the Migration library docs
[ci skip] Update the URI library docs
A tiny improvement in ruri_string()