Rplcd

This release primarily includes the pigpio backend (thanks sphh!) and a few
small improvements. Among other things, you can now use the I²C backend without
having the `RPi.GPIO` library installed!

- [add] Add pigpio backend (77)
- [chg] Limit GPIO cleanup to active pins (72)
- [chg] Add better help regarding missing `numbering_mode` (80)
- [chg] Late-import of GPIO backend in compatibility wrapper (78)

This is the first release that can be considered stable. It involves some API
changes, so you might need to adapt your scripts (mainly because some default
arguments to `CharLCD` were removed).

If you notice any documentation that hasn't been updated yet to the newer API,
please let us know!

- [add] Support for `MCP23008` and `MCP23017` I²C port expanders (43, 59)
- [add] Add `RPLCD.__version__` attribute
- [fix] Fix bug in auto linebreak algorithm (53)
- [fix] Fix bugs in show_charmap script (52)
- [fix] Fix error in A02 character map
- [chg] Remove default args for `gpio.CharLCD`, pins and numbering mode always
need to be specified explicitly from now on (60)
- [chg] Remove default for `i2c.CharLCD` i2c_expander parameter,
always needs to be specified explicitly from now on
- [chg] Remove all enums (`Alignment`, `CursorMode`, `ShiftMode`,
`BacklightMode`), replace them with string based API (67)
- [chg] Rewrite test scripts, expose them all through a single entry point
script: `lcdtest.py` (58, 59)

This version can be considered the release candidate for the 1.0 release.

- [add] Support for `PCF8574` I²C port expander (20)
- [add] Implement proper automatic encoding of unicode strings,
add encoding tables for A00 and A02 character maps (40)
- [add] Implement convenience functions for CR/LF (45)
- [add] Add documentation (37)
- [dep] Deprecate context managers (18)
- [rem] Drop support for Python 3.2

- [fix] Fix problem when auto-linebreaks clash with manual linebreaks (14)
- [fix] Fix wiring pin for GND (25)
- [add] Add option to disable auto linebreaks (14)
- [add] Add backlight GPIO control (21)

- [add] Implemented support for custom characters (4)
- [fix] Fixed a bug that caused offsets on 16x4 displays (16)

- [add] Removed all external dependencies
- [add] New ``show_charmap.py`` helper script