Prevent issues if sub-module would not be available + add is_numeric to int & float & ctype_digit to numeric
Fix typo
Add robots.txt
Better variation in floats
whitespace
Add 'to the power of' calculations to the arithmetic cheatsheet

(needs testing on PHP5.6)
Comment out `bcpow()` test as it breaks the sheets because of memory issues

Tested with `memory_limit` set up to 256M
Extend execution time for 'all' test pages