When an excessive amount of output is produced by the repl (for example
as a result of a rogue loop that is printing to stdout) Calva can
sometimes hang while trying to write all the output to the output
window/file.

The only way to resolve is to restart/reload the VSCode window.

This commit introduces a new config entry `replOutputThrottleRate` which
when set to a non-0 number will throttle output from the repl
connection. If more output items are received than the throttle rate in
a 500ms window then they will just be dropped.

Addresses BetterThanTomorrow#942
Fixes BetterThanTomorrow#2010

Calvas performance can be drastically affected as the size of the repl
output window grows.

This commit adds a config entry `replOutputMaxLines` which if set to a
non-0 number will cause the output window to be truncated if it grows
beyond this threshold.

Fixes BetterThanTomorrow#804

Co-authored-by: Peter Strömberg <[email protected]>