[logging] change "send" key to "sent" in http/ua

to be consistent with the two other logging calls
[logging] add post-facto filter

invoking .filter(contexts, name, filter) will apply ‘filter’ to the
object to be logged prior to writing

- context is a dot-separated list of context names (e.g., “ua.http”)

- name is the first parameter to the log call

- filter is either undefined, null, or a function

undefined = delete the filter
null = the null filter (do not log)
function(level, object)
[LOGGING] add level to object being logged

otherwise, we are dependent on the logging system not to lose it (not a
safe thing)
make indentation consistent
Merge branch `filtering` into `master`.