emacs: Split out the incremental json parser into its own function

emacs: Split out the incremental json parser into its own function

This patch splits out the incremental json parser into its own
function.

It moves the main logic of the parser to happen inside the parse
buffer rather than inside the results buffer, but makes sure all
results and all errors are displayed in the results buffer.

It also changes the local parser variables from being buffer
local to the results buffer to being buffer local to the parse buffer,
and sets them up automatically so the caller does not need to.

Finally to keep the diff small this patch does not fix the whitespace,
nor complete the code movement (these are done in subsequent patches)
but it should contain all the functional changes.