Omit "duplicated" abort checks, prealloc small ints, reduce copies, share symbol table

[xnacly]

• compiler: no per-instruction maps or operand slices, dead-code
  pass and constant deduplication
• vm: abort flag only checked on jumps and calls
• vm: builtins use a window of op stack instead of copied slice
• objects: Int values -128..1023 are preallocated
• objects: map iter presize key slice

With our workload (210 scripts importing a 26k-line library set) reduce compile time from 1371ms to 791ms:

benchmark	time	allocs/op
Compile	39.1ms -> 19.9ms (-49%)	884k -> 275k
VM geomean (13)	13.5ms -> 12.0ms (-11%)	534k -> 218k
VM/Fib	2.46ms -> 1.78ms (-28%)	75023 -> 21
VM/Builtins	28.6ms -> 16.7ms (-42%)	1.20M -> 398k
VM/StringOps	7.94ms -> 5.92ms (-25%)	395k -> 203k
VM/ArrayIndex	18.0ms -> 14.5ms (-20%)	998k -> 400k