add the parameter 'radix' to signedToString and unsignedToString
rename appendCStr to appendStr
add the method 'data' to StringBuilder and StringBuffer
add tests for 'data' and 'appendStr'
enable signedToString and unsignedToString to handle hex
introduce LIBJ_U and remove redundant String::valueOf
add new appendStr
make String::toUpperCase and String::toLowerCase more efficient
use LIBJ_STATIC_SYMBOL_DEF for memory efficiency