Custom transcript settings

This adds support for a custom transcript saving.

Users can now use -customtxt {format} to obtain a customised transcript. Format is a 7 digit (e.g. 1100100) string, representing (in order):
- Display start time
- Display end time
- Display caption mode
- Display caption channel
- Use a relative timestamp ( relative to the sample)
- Display XDS info
- Use colors

Default settings are:
0000101 for plain transcripts (only text)
1110101 for timed transcripts (times, mode + text at relative timestamp)
1111001 for the UCLA project (times, mode, channel + text at absolute timestamp)

Some examples of the output:
![ss 2014-07-01 at 09 54 06](https://cloud.githubusercontent.com/assets/7365586/3440360/368af936-00f6-11e4-8bb6-1edcc816ab6a.png)
![ss 2014-07-01 at 09 54 47](https://cloud.githubusercontent.com/assets/7365586/3440361/3695e6ac-00f6-11e4-86af-2dcf1f89b49a.png)
![ss 2014-07-01 at 09 55 16](https://cloud.githubusercontent.com/assets/7365586/3440362/36987746-00f6-11e4-8de4-5fceb5895de9.png)
![ss 2014-07-01 at 09 55 41](https://cloud.githubusercontent.com/assets/7365586/3440364/369c2210-00f6-11e4-84d0-a33bcb725121.png)
![ss 2014-07-01 at 09 56 14](https://cloud.githubusercontent.com/assets/7365586/3440363/369a12f4-00f6-11e4-8d40-f40dc1d66d48.png)

Fixes #15