Small tweaks.

added `range` to stdlib

tiny tweak (nonfunctional) to doctest.

small improvement to bool (runtime) type checking.
()
small improvements to handling booleans

clean up aggregators

crash handler hook (write repl lines)

hide ugly file names in error messages

more test cases added coverage target to makefile

added a few more test cases.
new infix operator for alist `->`/2

tweaks to list tests.
fixed force-directed layout.
merge.