Added quoted string literal output mode to strip.eel

The new -q switch will now use quote() on the final output, to
generate valid EEL/C/C++ quoted string literal output.

Fixed minor bug in strings.eel quote(), where STRINGS_MULTILINE
would issue an extra line with an empty string at the end.

Added EEL strip as the first option for generating builtin.c in
cfg-all.

Added builtin-bootstrap.c as a final fallback in cfg-all, if
both the EEL strip tool and sed fail.

Added test-stripped-quoted.eel to the test suite. It first runs
the EEL strip tool to strip, tokenize and quote the full test
suite, then loads the tests using io.read(), deserialize(), and
compile().

Closes #28.