these are the smaller improvements, they make about 5% worth of
difference

- use std::vector instead of std::deque
- use std::move on pendingCharacters instead of copying
- in FastAttributeList::add, when reallocate the buffer, allocate twice
the existing size, instead of increasing to only what we need
- in FastAttributeList, create getAttributeIndex and friends, so
we can avoid iterating the attribute list more often than necessary

Change-Id: I3e3380ea50b77c6845b66e83404e245778ec06eb
Reviewed-on: https://gerrit.libreoffice.org/57021
Tested-by: Jenkins
Reviewed-by: Noel Grandin <noel.grandin@collabora.co.uk>