Generate the documentation from include and doxygen/input only. Don't
get snared by files containing Doxygen comments that lie in other
directories such as tests, yotta, crypto/include, ...

The only difference this makes in a fresh checkout is that the
documentation no longer lists target_config.h. This file is from
yotta, does not contain any Doxygen comment, and its inclusion in the
rendered documentation was clearly an oversight.

Yotta is no longer supported by Mbed TLS, so has been removed. Specifically, the
following changes have been made:
 * references to yotta have been removed from the main readme and build
   instructions
 * the yotta module directory and build script has been removed
 * yotta has been removed from test scripts such as all.sh and check-names.sh
 * yotta has been removed from other files that that referenced it such as the
   doxyfile and the bn_mul.h header
 * yotta specific configurations and references have been removed from config.h

 * Change the Mbed TLS library version to 2.11.0
 * Increase the soversion of libmbedcrypto
 * Increase the soversion of libmbedtls

Bump SOVERSION for parity with 2.7.2 and 2.7.3.

Disable JAVADOC_AUTOBRIEF so that we can have periods in our brief
descriptions. We always use '\brief' where we want a brief, so this won't
hide any documentation previously used as a brief.

Remove the copyright block from the Doxygen comments, to clean up the
detailed description in the generated Doxygen output. Also, add \file and
\brief tags to all headers in doxygen/input.

When the Doxywizzard GUI is used and the doxyfile is loaded, the
workind directory for doxygen is set to the location of the doxyfile.
However the Make and CMake build systems expect doxygen to be ran
from the top level directory.
This commit unifies the build system and the Doxywizzard GUI so that
all of them expect doxygen to be executed in the doxygen directory.

We don't use symbolic links as part of our build process, so tell
Doxygen not to traverse them. In particular, if I have a symbolic link
to a directory outside the build tree, I don't want Doxygen to follow
it.

Previous change to include excluded the content in doxygen/input

Doxygen 1.8.10 warns that those tags are obsolete. Since we're not generating
XML anyway, it seems harmless to remove them even for earlier versions.

Changed version for library files and yotta module

Doxygen input file had incorrect function name for rng function
mbedtls_ctr_drbg_random(), and formatting was fixed.

 * Fixed incorrect file definitions
 * Fixed accidental tag problems in ecjpake.h
 * Corrected function naming in X.509 module definition

Changed for library and yotta module

Yotta version bumped to 2.1.3, as we had to do one more patch release to the
yotta registry to accommodate for dependencies updates.

Even if they don't need it: this simplifies future audits.

- most in doxygen doc that was never renamed
- some re-introduced in comments/doc/strings by me