This change is a result of a discussion thread on freetype-devel

  http://lists.nongnu.org/archive/html/freetype-devel/2015-06/msg00041.html

Re-introduce the `freetype2' subdirectory for all FreeType header
files after installation, and rename the `freetype2' subdirectory in
the git repository to `freetype'.

* include/freetype2: Renamed to...
* include/freetype: This.

* CMakeLists.txt (PUBLIC_HEADERS, PUBLIC_CONFIG_HEADERS,
PRIVATE_HEADERS): Updated.
Update creation of `ftconfig.h'.
Install generated `ftconfig.h'.

* Jamfile (HDRMACRO, RefDoc), autogen.sh: Updated.

* builds/amiga/include/config/ftconfig.h, builds/freetype.mk
(PUBLIC_DIR), builds/symbian/bld.inf, builds/toplevel.mk (work),
builds/unix/freetype2.in: Updated.

* builds/unix/freetype-config.in: Updated.
* builds/unix/configure.raw: Don't check for `rmdir'.
* builds/unix/unix-def.in (DELDIR): Use `rm -rf', which is portable
according to the autoconf info manual.
* builds/unix/install.mk (install, un...