Replace *strhti*, *strfind*, *hexstr*, and *endswap* functions in gbdbrsp module

[andersondomingues]

Auxiliary functions in gdbrsp module must be replaced by corresponding functions in std library or moved to outside the gdbrsp module.

functions:
strhti => converts an string represented hexadecimal number to its integer representation
strfind => find the index of some character in the character string
hexstr => converts a bytestream to its hexadcimal string representation
endswap => byte swap for endianess treatment