jsdbgapi Enhancements

TBD Add link to list of abilities in existing api.

Enhancement ideas...

• Convert numerous get/set hook calls to a 'block of hooks' api.
• Add api to fill array of bit flags indicating which souce lines of a script have executable code; i.e. where breakpoints can be set.
• Add api to iterate trynotes; i.e. to figure out ranges of lines protected by try blocks.
• Add api to get pc of catch for a given pc in script (or null if none). To distinguish caught from uncaught exceptions (before the stack unwinds).
• Add watchpoint iterator and finder.
• Write srcnote for 'end of block' to make script ranges include trailing lines that don't happen to have code.