Reworked documentation generation and installation.
Details:
- Remove configure flag used to disable the automatic generation of the
documentation when istalling.
- Now 'make html' generates the documentation.
- Now 'make install' does not install the documentation, 'make install-html'
does that. The latter two changes follow newer automake conventions.
- This also fixes the bug that caused the documentation missing from the
tarball.

 prefix=@prefix@

 exec_prefix=@exec_prefix@

 libdir=@libdir@

 includedir=@includedir@

 Name: @PACKAGE_NAME@

 Description: Library of Efficient Models and Optimization in Networks

 Version: @PACKAGE_VERSION@

 Libs: -L${libdir} -lemon @GLPK_LIBS@ @CPLEX_LIBS@

 Cflags: -I${includedir} @GLPK_CFLAGS@ @CPLEX_CFLAGS@