* Add an abstract class "Option", and basic subclasses : "OptionInt",
"OptionDouble", "OptionString".
* Add "optionChecker" app, which parses AVOptions of a CodecContext and
create an array of Options.
* Update SConscripts to add "src/AvTranscoder/Options" folder, and
compile "optionChecker" app with c++11 flag.

…scoder into dev_audioProcessing

* Corresponding to AV_OPT_TYPE_FLAGS in libav / ffmpeg.
* Manage AV_OPT_TYPE_FLOAT and AV_OPT_TYPE_DOUBLE by the same way :
create "OptionDouble".
* Add const to the getDefaultValue function of "OptionString".

* Corresponding to AV_OPT_TYPE_RATIONAL in libav / ffmpeg.
* Create a struct Value2D to get the defaultValue of this option by one
call of getDefaultValue (which returns a Value2D).

* Corresponding to AV_OPT_TYPE_FLAGS with unit informed in libav /
ffmpeg.
* Update optionChecker to create OptionGroup, and continue to parse if
meet unknowed AVOption type.
* Update comments of OptionBoolean.

* Corresponding to AV_OPT_TYPE_INT with unit informed in libav / ffmpeg.
* Update optionChecker to create OptionChoice, add list of choices to
them, and set their default choice.
* Option: add unit attribut.
* Subclasses Option: update getType function to return a string instead
of an enum defined in libav / ffmpeg (AVOptionType).

* Update optionChecker to fill OptionGroup by OptionBoolean.

* Rename appendOption by appendChoice.
* Update @brief of the class.

* Suppress tabulation.

* Rename Option2D by OptionRatio.
* Use std::pair<int, int> instead of custom struct Value2D.

* Update optionsChecker to use the OptionLoader. The app calls the
loader and displays the list of options.

* 2 new params:
	* req_flags
	* rej_flags
* Can manage specific AVOptions depending on their flags.

* Option class is not abstract anymore: it represents all possible type
of Option (Int, Boolean, Choice...).
* OptionType enum manages the different cases of option (Int, Boolean,
Choice...).
* Option class contains an array of Option: contains sub options in case
of Choice or Group.
* OptionLoader manages an array of Option (instead of pointers).
* OptionChecker doesn't need to include libav / ffmpeg files
(thankfully).
* Update SConstruct: Options folder doesn't exist anymore.

* Update avinfo app to call functions defined in Description.hpp.

* Use constant member functions as much as possible.
* Return const elements when getting sub options of a Group or a Choice.

* In loadOptions function, choose what ffmpeg / libav object on which
we'll scan AVOption: avFormat or avCodec.
* Update OptionChecker app: no need to get a codecContext from the
audioDesc of a stream of an InputFile !

* Also parse name, because name's format defines (in general)
extensions.

* Sort array of extensions.
* Suppress duplicates.

* Fix algo when parse extensions.

* This app checks getInputExtensions and getOutputExtensions functions.