Attempt to define AVT and TVT; removed spurious FIXME:
added build badge to README
Merge pull request #124 from xquery/xproc20

added build badge to README
Merge pull request #125 from ndw/avt-tvt

Attempt to define AVT and TVT; removed spurious FIXME:
Attempt to address Alex's comments on the pre-FPWD draft
Merge AVT/TVT changes into this draft
Merge pull request #126 from ndw/alex-review-20141203

Alex's review comments on the proposed FPWD.
Merge Alex's review comments and AVT/TVT updates into the FPWD draft