parsing of negative numbers - resolves #59

can now represent, using Prolog syntax, the minimum possible value of a
long primitive: -9223372036854775808
added between/3 - resolves #43
added writef/2 -resolves #41
supported testing of new lines in output
added nth0/3, nth1/3 and nth/3 - resolves #44 #60
atom_concat/3 - resolves #7
append/3 - resolves #23
added predsort/3 - resolves #61