Ideas for invocation / usage:

* query param _scrutinize=1
** Debugger UI for that request
** Step, break, eval, etc
** At exit display output from execution

* /_scrutiny/ injected URL
** List current stopped sessions
** Select a session to debug
** Add global breakpoints
*** Breakpoints on specific code lines
*** Breakpoints on watch variable
*** Breakpoints based on URL
** List URLs for easy selecting for breaking
** Code browser for setting breakpoints

* Inline with in-code breakpoint
** Code calls Scrutiny::break()
** Show debugger UI
** could also turn die() into break?

UI
* Code browser
** Numbered lines
** Breakpoint set / show
** Roll-over / click to view variable values?
** Highlight current execution line
* REPL
** Interactively execute code
** Interactively inspect
* Watch Log
** view log of watched variable changes
* Execution log
** View log of lines-executed
** Walk forward/backward over lines