Minor bugfixes, causing however an ABI change.

* fixing incorrect string length calculation in HitachiLCD when used
with screen width calculation and non-ASCII UTF-8 chars. This fix
changes the library’s ABI and API, so please recompile your code with
the new API.
* Making the I2CError exception a type of its own.
* Making sure InputObjects can be restarted after stopping them
manually with stop().
* now using the actual pointer size in address offset calculation for
the GPIO registers - expecting a 64 bit OS for the Raspberry Pi 3 some
time later.
* removing unused, and badly designed string read function from
AutoFile.

fixing missing ldconfig in make install, correcting the code samples …

…for the main() return type, streamlining demo.cpp