Document differences of post-mortem debugging using dump.frames vs tryCatchLog

[aryoda]

Standard R also supports post-mortem dumps + debugging, see the description here:

https://cran.r-project.org/doc/manuals/R-exts.html#Debugging-R-code

... find out more about what was happening at the time of the crash by looking a post-mortem dump.
To do so, set options(error=dump.frames) and run the code again.
Then invoke debugger() and explore the dump.
To do so, set options(error=dump.frames) and run the code again. Then invoke debugger() and explore the dump.

Because last.dump can be looked at later or even in another R session, post-mortem debugging is possible even for batch usage of R.

Post-mortem debugging is good for finding out exactly what went wrong, but not necessarily why.
An alternative approach is to take a closer look at what was happening just before the error, and a good way to do that is to use debug.
This inserts a call to the browser at the beginning of the function, starting in step-through mode.

Document the differences + usage recommendations

[aryoda]

Could be done together with #48

[aryoda]

Releated to #78