Closure Optimizations and Loop Unrolling

 * tail-call optimization is reported only when a tail call is marked
 * `toString()` of inline functions and function items now shows the closure
 * higher-order functions are not pre-evaluated any more (could do arbitrary things at compile time)
 * static bindings in the closure of inline functions are now always inlined
 * `fn:fold-left(...)`, `fn:fold-right(...)`, `fn:for-each(...)` and `hof:fold-left1(...)` are now unrolled if the sequence they iterate over is static and has less than `FNFunc#UNROLL_LIMIT` items