Add Travis-CI configuration file

Signed-off-by: Gregory Petrosyan <gregory.petrosyan@gmail.com>
Add Travis-CI badge to the README.md

Signed-off-by: Gregory Petrosyan <gregory.petrosyan@gmail.com>
make enum and array in options.c independent of order

When the enum `format_id` and the array `str_defaults` are used in the functions `options_add` and `options_load`,  both have to be in the same order for the code to work.
The code breaks silently if this is not the case.

This patch removes this dependence and moves the array (which is currently 1000 lines away) right next to the enum to make the connection between these two structures clear.
added some whitespace to str_defaults
make sure that array elements without a designator don't overwrite previous elements
Merge pull request #61 from mahkoh/fmt-enum

make enum and array in options.c independent of order
travis-ci: add libavformat-dev and libopus-dev

Signed-off-by: Gregory Petrosyan <gregory.petrosyan@gmail.com>
travis-ci: remove libopus-dev, since Travis' Ubuntu does not yet have it

Signed-off-by: Gregory Petrosyan <gregory.petrosyan@gmail.com>
Merge branch 'master' into show-all-tracks