Changes:
* Implement patty_ax25_if_driver type, providing a vtable with
pointers to methods implementing an AX.25 interface PHY
* Implement patty_ax25_if_name() to return a pointer to the name
string of an AX.25 interface
* Decouple patty_kiss_tnc from src/if.c using patty_ax25_if_driver
* Remove port input/output arguments from patty_kiss_tnc_send()
and patty_kiss_tnc_recv(), respectively; use 0 as the default,
but keep the port argument in patty_kiss_frame_send()
* Implement patty_ax25_if_fd() to return file descriptor backing a
PHY; use this rather than patty_kiss_tnc_fd() in src/server.c to
further decouple interfaces from their implementation
* Remove 'enum patty_ax25_if_type' type; refactor constructor
patty_ax25_if_new() to no longer take this as an argument, but
rather a patty_ax25_if_driver to use to instantiate the PHY
with the information pointer passed
* Break out patty_kiss_tnc code from src/kiss.c into src/tnc.c,
leaving only patty_kiss_frame_send() in the original; this is
needed to prevent a cyclic dependency within patty_ax25_sock and
other areas
* Rename patty_bin_if_config() to patty_bin_if_create(); a separate
patty_bin_if_config() will likely be created later as necessary
to change an existing interface
* Split PHY-specific interface configuration code into separate
delegates in bin/if.c
* Implement usage of patty_error to better capture internal error
states not currently representable with semantic error numbers
while configuring and instantiating PHYs
* Pass patty_error object to patty_bin_kiss_config() to receive
detailed error information
Changes:
* Move network interface configuration logic from bin/pattyd.c to
bin/if.c; implement a more robust state machine
* Move KISS TNC configuration code from bin/pattyd.c to bin/kiss.c
* Ensure configuration file name, line number, and erroneous part
of an expression are clearly indicated upon failure
Other changes:
* Improve bin/Makefile to rebuild objects when accompanying header
files change
* Refer to HEADERS_SUBDIR, not HEADER_SUBDIR, in Makefiles
