This is instead of caching it inside nilmdb.server.wsgi_application.
Might make things work a bit better in case the web server decides
to call wsgi_application multiple times.

This way, errors like "database already locked" can be fixed and the
page reloaded, without needing to restart Apache.

When enabled, lines like "# interval-start 1234567890123456" and "#
interval-end 1234567890123456" will be added to the data output.  Note
that there may be an "interval-end" timestamp followed by an identical
"interval-start" timestamp, if the response at the nilmdb level was
split up into multiple chunks.

In general, assume contiguous data if previous_interval_end ==
new_interval_start.

Added new flag "-R" to command line to perform an automatic removal.
This should be the last of the ways in which a single command could
block the nilmdb thread for a long time.

Server class will retry as needed, as with stream_extract and
stream_intervals.

Implemented in command line, client, server, nilmdb, bulkdata

Also changes the HTTP parameter from "extent" to "extended",
and the commandline parameter from "extent" to "ext".

"import nilmdb" doesn't do much; "import nilmdb.client" or "import
nilmdb.server" is now required.

The server buffers the string and passes it to nilmdb.  Nilmdb passes
the string to bulkdata.  Bulkdata uses the rocket interface to parse
it in chunks, as necessary.  Everything gets passed back up and
everyone is happy.

Currently, only pyrocket implements append_string.

Replaces custom tools.allow_methods which didn't return the Allow: header.

This will help amortize the sqlite synchronization costs.

Only tested with v1.1.0.  It's not clear how well older versions will
work.

This is a pretty big change that will render existing clients unable
to modify the database, but it's important that we use POST or PUT
instead of GET for anything that may change state, in case this
is ever put behind a cache.

Dependencies should be handled by installation, not at runtime.

It's only the server that calls it in multiple threads.

This decorator makes a class always be serialized, including its
instantiation, in a separate thread.  This is an improvement over
the old Serializer() object wrapper, which didn't put the
instantiation into the new thread.

Previously, we could get empty intervals anyway by having a non-empty
interval and removing a smaller interval around each piece of data.
Turns out that empty intervals are OK and needed in some situations,
so explicitly allow and test for it.

Previously, we allowed start == end, but this doesn't make sense with
half-open intervals.

Previously some functions returned the string "ok".

Update tests accordingly.  This isn't backwards compatible, but
existing clients don't rely on it.

Specifically, switch from using global configuration and several apps,
to using application-specific configuration with a single app.  This
should hopefully make it easier to plug this into another
WSGI-compliant server someday, and also silences some startup warnings
about missing application configs.

Now nilmdb.client, nilmdb.server, nilmdb.cmdline, and nilmdb.utils
are each their own modules, and there is a little bit more of a
logical separation between them.  Various changes scattered throughout
to fix naming (for example, nilmdb.nilmdb.NilmDBError is now
nilmdb.server.errors.NilmDBError).

Reduced usage of "from __future__ import absolute_import" as much
as possible.  It's still needed for the functions in the nilmdb/server
directory to be able to import the nilmdb module rather than the
nilmdb.py script.

This should hopefully ease future packaging a bit.