There are now four ways that CBT can be disabled:
1. Network-wide, with the cbtdisabled consensus param.
2. Via config, with "LearnCircuitBuildTimeout 0"
3. Via config, with "AuthoritativeDirectory 1"
4. Via a state file write failure.
All other bandwidthrate settings are restricted to INT32_MAX, but
this check was forgotten for PerConnBWRate and PerConnBWBurst. Also
update the manpage to reflect the fact that specifying a bandwidth
in terabytes does not make sense, because that value will be too
large.
This should be a very faithful conversion, preserving as much of the layout
of the old manpage as possible. This wasn't possible for the nt-service
and the DataDirectory/state parts. See a later commit for some small
cleanups.
Tiago Faria helped with the asciidoc conversion, big thanks!
