Work on the Attribute module

[nm17]

Currently a draft, any comments are welcome!

[nm17]

Oh, and I forgot to cargo fmt. I will do it after, I just didn't want to screw something up.

[nm17]

Next up I will try to document GattServer and stuff related to it. Then I will:

• try to split the AttributeData read and write functionality into a separate trait
• try to make ServiceBuilder::add_characteristic_internal public, but use the trait I added as a dyn type.

[nm17]

Also, related issues: #98 #35

[nm17]

I have no idea how the error[E0597]: bat_level does not live long enough error came to be in example/apps/ble_bas_peripheral.rs. I would like some help with this. I don't think that I've yet changed anything in how the AttributeData works...

[HaoboGu]

I have no idea how the error[E0597]: bat_level does not live long enough error came to be in example/apps/ble_bas_peripheral.rs. I would like some help with this. I don't think that I've yet changed anything in how the AttributeData works...

I encountered similar error before, see #95 . But I'm not sure whether this is your case. There're some complex lifetime calculations.

[lulf]

The attribute modules have changed a lot since this initial PR, and I think some of the original feature requests around making the attribute server optional (supported) as well as more control over how to handle/reject requests in attribute server is resolved. Is there a reason to keep this open?