Memory leak in proj lib documented.

There seems to a memory leak in the proj lib, oh well...
Add ostream output and functions to get first and last times to Timestamp.
Collector::read_relations() can be called with iterators, too.
Comment out debug output.
Make initial buffer size in PBF reader much smaller.

Especially blocks containing nodes can be quite small.
Add osmium::io::read_file() function to read file in one go.
Improve iwyu report.
Unify operator<<

- Use #include <iosfwd> everywhere which should be enough for operator<<
- Use basic_ostream instead of ostream or a template parameter

The templetized version of operator<< wasn't a good idea. We didn't have
to include <iosfwd> that way, but for some uses we get compiler errors
because of ambiguous overloading.
Short-circuit 4326 projection and do rad_to_deg conversion for latlong CRS.
Make manipulators work with VerboseOutput.
Add function to extend box with another box.
Refactor check_includes and iwyu targets.

They create their report file by file now which means they only have to
re-create what has been changed.
Remove internal namespaces and files from docs.

Everything in namespaces names "detail" and in directories names
"detail" is internal to libosmium and should not be used by users.
Make IdentityProjection a class and document it.
Fix setting of user attribute when reading changesets from XML.
Make sure DiffIterator is always based on an iterator over OSMObjects.
(de)compressor code cleanup.
Bugfix: Close file opened with bzReadOpen() with bzReadClose().
Open files in binary mode in bzip2 (de)compressor.
Add error checks and fixed reading bug in bz2 (de)compressor.