* scheme-using.texi (Error Handling, Interactive Debugger): Minor

* scheme-using.texi (Error Handling, Interactive Debugger): Minor
editorial improvements.
(Leave Debugger): Removed.
(Display Backtrace): Minor updates.
(Frame Selection, Frame Information, Frame Evaluation) : Minor
editorial improvements.
(Stepping and Continuing): Merged from three previous nodes; plus
minor improvements.  Removed doc for `trace-finish', which no
longer exists.

* debugging/ice-9-debugger-extensions.scm (debugger:step):
Docstring improvements.
(debugger:next): Docstring improvements.
(debugger:continue): Docstring improvements.

* debugger/commands.scm (up, down): Docstring corrections.
(info-args, info-frame, position, evaluate): Docstring
improvements.