add memory limit support in phpctags

Use the known memory limit adjustments (-1, positive integers or bytes
and human readable sizes) to adjust the memory used during the parsing
and lexing that occurs in phpctags
Rename the function to 'isMemoryLimitValid'
Only set default memory limit if it's not set
Merge branch 'feature/add-memory-limit' into develop

Fix #6
Update the credits
Fix autoloader.php path
Merge branch 'feature/fix-autoloader-path' into develop

Fix #8
Use a more generalized shebang line
Make -f option work as expected
Add support for -a option
Add support for --append option
Add support for -R option
Add support for --recurse option
Add support for --exclude option
Merge branch 'feature/improved-console-support' into develop

Fix #9
Merge branch 'develop' into feature/add-memory-limit
Set memory limit in the executable script

It is not part of the "PHPCtags" class' functionality.
Merge branch 'feature/add-memory-limit' into develop
Merge branch 'develop' into feature/improved-console-support
Ensure -R option only applies on directory