[PATCH 0 of 2 RFC] c-hglib: hg_log() level 1 function (introduction)

[Iulian Stana]

This is a draft of my work for c-hglib up to now, I am sending this to the list
for public review (even if this is not a patch for the core mercurial). I am
sure that the main developers following my work (Matt, Pierre-Yves, Idan and
others) will have important remarks on the architecture and on the style, and I
like to solicit those feedbacks.
This patchbomb will show the implementation for hg_log command using an
iterator-like mechanism.