refactored parsing functions to be more pointer-safe
refactored promp function to return a command that represents both variable assignment and actual command
basic command parsing implemented, missing variable expansion, string and escape sequences resolution.
implemented path resolution, minor fix in error.c, added env var helpers, profile file is now free of errors
refactored environment variables list into environment_t
execve and fork support
fixed wrong malloc length with some string length not considering null byte
experimental variable expansion, to be moved to expansion of variables inside {} brackets
fixed cd bug in parseSpecial