Added strDirname(), which returns the directory path name from the given string.
Added str2int(), which converts from the string to the integer.
These functions are used to supplement the existing string manipulation functions in the utils/str module.
The math.h was included before the _USE_MATH_DEFINES
was defined (in tvgMath.h) causing an error while
MinGw was used.
Since non of these header is needed directly, the header
is removed.