[DOC] add fixed fee docs to payments API
[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.
[DOC] REST - warning about limit=all timeouts
Merge pull request #102 from boxbag/fixed-fee

[DOC] add fixed fee docs to payments API
[DOC] REST - fee clarification