- Added error severity, mainly to distinguish between READ and EVAL
errors, can be later expanded to allow other distinction
- Improved repl using the above function (EVAL errors interrupts the
repl right away, without the need to double-return)
- Added an helper function to provide infos about builtin and composed
functions
- Possibility to pass files as arguments to setup the environment
Signed-off-by: teo3300 <matteo.rogora@live.it>