Added equals assignment operator

The set phrase will be removed and just replaced with a single
equals sign. Double equals will be used for comparison. This will
be much easier to understand.

tests/lexer/all.arf

@@ -1,3 +1,3 @@
 :arf
 --- rw -> -349820394 932748397 239485.37520 "hello world!\n" 'E' helloWorld:.,..[]{}
-+ - ++ -- * / @ ! % %= ~ ~= = != < <= << <<= > >= >> >>= | |= || & &= && ^ ^=
++ - ++ -- * / @ ! % %= ~ ~= = == != < <= << <<= > >= >> >>= | |= || & &= && ^ ^=