Call AM_INIT_AUTOMAKE once

It is actually invalid to call AM_INIT_AUTOMAKE several time, and
provokes an error.
updated OSX build doc to use Autotools (easier)
Add doc to build on gentoo with overlay
highly experimental soft checkpoint based on consensus
Merge pull request #99 from toyg/new_osx_build_doc

updated OSX build doc to use Autotools (easier)
Merge pull request #98 from jd/jd/fix-build

Fix AM_INIT_AUTOMAKE call
Merge pull request #104 from ddorian1/doc

Overlay for gentoo