Rename to_string

Renamed to_string to c_str
Lower case 'a' in array.h
Added MIT header
Added MIT header
Unit test for 'function'
Added back() & #error for base class
Added stack container class
Added back() tests
Added pow<> template

Compile time calculation of powers.
Edited comments
Added container orientated functions
Added cyclic value class
Changed Math to Maths
Added project logo
File name change
Added vector class
Added nullptr definition
File rename
Added largest type/size template
Added numeric file

Defines etl::iota