[jayes] better XDSL format performance

- completely removed XPath usage from XDSLReader
- no more String.format in both writers

Change-Id: I580bf22bb2b33c0f8e63bf9b471e9431413fa553
[jayes] IO benchmarks

Change-Id: Ib3c76979e30a3b961bfa35146a1e0e8f50802f03