Added letin program.
Fixed.
Added error_to_string.
Fixed.
Added load2 for one argument.
Added first test for compiler and fixed somethings.
Changed vector of errors to list of errors.
Fixed error complaining.
Added two tests.
Added test and fixed somethings.
Changed syntax.
Added two tests and fixed somethings.
Fixed.
Added tests and fixed somethings.
Fixed.