Add proper support for "piqic-erlang --normalize-names true|false"

This option became broken after piqic-erlang was rewritten in Erlang on top of
"piqi compile".
Fix: use piqi exectuable from priv/piqi-binary/... during the build
Import piqi-erlang documentation
Use $PIQI as the location of the "piqi" excutable (when defined)
Fix tests