Accept input file name on candump2analyzer command line.

If an argument is given to candump2analyzer, try to use it as the
input file name instead of standard input.  If that fails, return
error exit code 1.
Do not rely on fixed CANDUMP_DATA_START.

Just in case the CAN ID or size fields have a non-standard length, try
to find the data start point by looking for the first non-space
character after the closing bracket.
Increase buffer size for Fast-Packet data.

Set MAX_DATA_BYTES to 223, which is the maximum length of a full
Fast-Packet payload package.  Also check the buffer size to avoid
overflowing.
Merge pull request #25 from acolomb/candump-improvements

Extend functionality for candump2analyzer tool