Host requeriments

- Free space needed at host:
  - For toolchain creation: around 2.6GB 
  - For kernel creation: around 800MB by/per kernel
  - For building ports: 1.4GB 
- Minimal version required of some components:
  - Kernel:
  - gcc:
  - glibc:

- Notes for some host distros:

  - Install build-essential, m4, git-core, texinfo, libarchive-dev, bsdtar, gperf and gawk packages.
  - core-ports:  bison (1), groff (2), flex (3), help2man (4) .
   - (1): Needed by findutils.
   - (2): Needed by groff.
   - (3): Needed by iproute2.
   - (4): Needed by sed.
   - iputils: problem with xz and libarchive.
  - Fixed build ports with fakeroot adding the path to /usr/lib/libfakeroot to LD_LIBRARY_PATH.
  - Fixed the link to pkginfo/pkgadd at pkgutils-cross dir.
  - Fixed docs to adapt it to those changes.