Subtitles Round 3

[dinkypumpkin]

I've refined things slightly to combine all those new boolean options 
(dunno what I was smoking when I did that) into a single --subsfmt 
option.  I've included below the relevant section from the draft release 
notes to describe the values of --subsfmt.  This is what I'm going to go 
with, barring any bugs discovered in the next few days.

As before, I've posted a patched version of get_iplayer here:

https://raw.github.com/dinkypumpkin/get_iplayer/feature/subtitles/get_iplayer

The patch against master branch is here:

https://github.com/dinkypumpkin/get_iplayer/compare/feature;subtitles.patch

Draft release notes section for subtitle changes:

### Subtitle Fixes and New Formats

Around mid-September 2013, the BBC began producing subtitles in a new 
file format that broke get_iplayer's translation from TTML to SRT. 
get_iplayer has been updated to accommodate the new file format.

A new `--subsfmt` option has been added to offer alternative formats for 
subtitles.  This option accepts one of the following values:

**default** (or unspecified):  Line break followed by leading hyphen 
demarcates change in speaker.  All other line breaks removed, so lines 
must be wrapped by media player.  Text rendered in default subtitle 
colour for media player.  This is the same format used in get_iplayer 
2.83 and below.  If your media player cannot wrap text, use one of the 
other formats below.

**break**: Like **default** except that line breaks in subtitles file 
are retained.  This may lead to some awkward formatting due to the extra 
line breaks inserted for changes in speaker. Only use this format if 
your media player cannot wrap text but you still prefer the **default** 
format speaker change demarcation.

**basic**: No demarcation of change in speaker.  All line breaks 
retained.  Text rendered in default subtitle colour for media player. 
The is the format used in the Flash player on the iPlayer site.

**compact**: Leading hyphen (without line break) demarcates change in 
speaker.  All line breaks retained.  Text rendered in default subtitle 
colour for media player.

**colour** (or **color**): Change in text colour demarcates change in 
speaker.  All line breaks retained.  Text rendered in colours defined in 
subtitles file.  Any text for which a colour cannot be ascertained is 
rendered in default subtitle colour for media player.  If your media 
player does not support subtitle colours, all text is rendered in 
default subtitle colour for media player.  This format is roughly the 
same as that used for subtitles on broadcast television.

**Reminder**: If you wish to change the format of subtitles for a 
particular programme, you can re-download only the subtitles for the 
programme with:

get_iplayer --subtitles-only --overwrite --subsfmt=<format> --get <index>

OR

get_iplayer --subtitles-only --overwrite --subsfmt=<format> --pid <PID>		


##### Caveats

The **compact** format has no effect for subtitles in the new file 
format referenced above.  The subtitles do not have any structure that 
can be used to ascertain changes in speaker, so the output is same as 
with the **basic** format.

The **colour** format has (almost) no effect for subtitles in the new 
file format referenced above.  Although the subtitles have colours 
defined, the same colour (white) is used for all of them. The subtitles 
do not have any structure that can be used to ascertain changes in 
speaker, so the output is the same as with the **basic** format, with 
the exception that all text is rendered in white.

You may still set `subfmt` to **compact** or **colour** in your 
preferences in order to use those formats with programmes subtitled 
before mid-September 2013.  They will just be effectively ignored for 
programmes subtitled after that date.