[DOC]: Ripple-REST Update balances and trustlines limit query param

- Allow ?limit=all
Merge pull request #103 from lumberj/doc/limit_all

[DOC]: Ripple-REST Update balances and trustlines limit query param (RLJS-116)

I'll add an explanation that using limit=all might cause timeouts, but I recommend in the long term setting some explicit limits and handling the error gracefully.