libgpiod: bump version to v0.3

libgpiod: bump version to v0.3

Add host-pkgconf to dependencies as we now use PKG_CHECK_MODULES in
configure.ac.

Changelog for v0.3:

New features:
- gpiomon can now watch multiple lines at the same time and supports custom
  output formats which can be specified using the --format argument
- testing framework can now test external programs: test cases for gpio-tools
  have been added

Improvements:
- improve error messages
- improve README examples
- configure script improvements

Bug fixes:
- use correct UAPI flags when requesting line events

Also includes bug fixes from v0.2.1:

Bug fixes:
- capitalize 'GPIO' in error messages in gpioset, gpioget & gpiomon
- tweak the error message on invalid arguments in gpiofind
- don't ignore superfluous arguments and fix the displayed name for falling
  edge events in gpiomon

Signed-off-by: Bartosz Golaszewski <brgl@bgdev.pl>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>