Correct help message inconsistencies.

  Enclose -fstack-size suffix in [ and ] to better tell it is optional.
  Add missing ending } character to -fuse-semaphore help.
Rename function names clashing with system headers.

  Depending on system headers included some symbols would clash with
macro names, and have been renamed.
Add new hashtable primitive with vector like usage and syntax.

  Hash tables are common and useful enough to have the language
providing an easy interface to them, and using vector syntax make
usage easier.

  The special conditions that may look uncommon at first are:
o "table[something] = null" is the idiom to remove an entry; noop
  if there is no such entry
o "table[null] = something" generates an exception, null is not
  allowed as a hash key
o "table[invalid_key]" as rvalue returns null, not an error if
  key does not exist
o "++table[invalid_key]" generates an exception as well as
  "table[invalid_key] += 2", but
  "table[invalid_key] = table[invalid_key] + 2" works, because
  it expands to
  "table[previously_invalid_key] = null + 2", and null is coerced
  to zero.