some issues encountered when learning to use janet's peg system

gistfile1.txt

* the return value of `peg/match` is either `nil` -- which means that overall
  matching failed (though submatches might have succeeded) -- or an array
  that can contain matches (see below for more details).  many of the 
  initial examples don't actually "capture" though so one keeps seeing
  an empty array as a return value.

* `peg/match` does do matching, but it also "captures" along with the ability
  to perform essentially arbitrary computations on values that are "captured".
  so the name `peg/match` might be seen as a bit misleading.

* the name "capture stack".  it's true that there is a stack on to which
  things get captured, but this is not all that happens there.  stuff can
  get removed via `drop`.  stuff can be replaced by `group`.

* had difficulty with the names `*` and `+` (which appear inherited from 
  lpeg) due to these being used to mean quite different things in the 
  context of regular expressions.  luckily, one can use `sequence` and 
  `choice` instead and gradually get used to them.
  
* no name for the idea of the index / spot that the matching is about to
  take place at.  many references in the documentation say "advances" or
  "does not advance", but it is kind of awkward to not have something one
  can refer to which is or is not advancing.
  
* there is no tracing for `peg/match`.  it's a black box.  it's powerful, but
  not really easily subject to introspection (it is possible via gdb fwiw).