fix doc block get_request_header()

This method does not return FALSE as said in doc block, the correct
return is STRING or NULL.
Merge pull request #3262 from adrianorsouza/pr-fix-doc-input-class

fix doc block get_request_header()
config_item() to return NULL instead of FALSE for non-existing items

Close #3001
Close #3232
Related: #3244
Optimize the composer_autoload check
E_DEPRECATED is not available in PHP 5.2
Update a config_item() use case for the new NULL return value
Attempt a better base_url auto-detection
#3253
Fix #3270

Related: #3268, 4bdb66759c24c41fefec7952b12a0595a671eaa2
Fix Config_test::test_base_url()
Escape arrays sent as binding values for database queries.
Escape the array elements separately and join them in compile_binds()
Update the change log and the documentation with the array values binding feature.
Update mimes.php

Updated a mines for file format ical. Although it is the same as ics the upload library should also recognize ical file format just the same.
Close #3280
Reword change log and add the resulting query in the manual.
[ci skip] Fix Travis build status badge

It broke with the repo transition.
[ci skip] Update 2 links to relate to bcit-ci/
Merge pull request #3282 from SirDre/patch-3

Update mimes.php
Merge branch 'develop' of github.com:bcit-ci/CodeIgniter into develop