Many small improvements

[MarioIvancic]

I've added a couple of improvements (in my opinion) to ttylog:

• More baud rates, up to 4 MHz (if supported by the system).
• Reimplemented timeout feature without librt.
• Option -F|--format to set output format to ascii, raw, hex or HEX.
• Option -l|--limit to limit output line length (for ascii or raw) or byte count (for hex).
• Option -m|--mode to set serial port mode (data bits, stop bits, parity).
• Option --rts to set RTS Line state.
• Option --dtr to set DTR line state.
• Optional argument to -s|--stamp option to set timestamp format.

Output format can be:

• ascii like is is now,
• raw like ascii but \r is not ignored and read() is used instead of fgets(),
• hex lowercase hex,
• HEX uppercase HEX.

Timestamp format can be:

• old like it is now,
• iso for ISO-8601 YYYY-MM-DDTHH:mm:ss.sss,
• ms for number of milliseconds from program start, 9 digits in 3 groups, nnn.nnn.nnn,
• us for number of microseconds from program start, 12 digits in 4 groups, nnn.nnn.nnn.nnn.

If not specified old format is assumed.