C++ wrapper for vte, version 0.25.0.

Current dependencies:
- to build a library from tarball:
  * vte >= 0.26.0
  * glibmm-2.4 >= 2.22.0
  * pangomm-1.4 >= 2.24.0
  * gtkmm-2.4 >= 2.20.0
  * giomm-2.4
- to build a documentation:
  * same as above and tools required by mm-common, that are:
    - perl
    - doxygen
    - dot
    - xsltproc
- to build in maintainer mode:
  * same as above and tools used by maintainer:
    - git (to generate a ChangeLog)
    - mm-common >= 0.9.5
    - recent autotools because no deprecated macros are used.