Abstract away the difference between a download and a download result, i.e. remove and purge

[pawamoy]

I think it would make aria2p easier to understand and use. Currently we "remove" downloads and "purge" download results. I'd like to get rid of the "purge" methods and only use "remove". The "remove" methods would be smart enough to know if we have to internally purge or remove, based on the download object status.

I think it would simplify things, but maybe it's a not a good idea. Any thoughts, users of aria2p?

[pawamoy]

I went ahead and planned things like this:

• deprecation warnings are immediately added to API.purge, API.purge_all and "purge" command
• in version 0.7.0, API.purge, API.purge_all and "purge" command are removed
• change warnings are immediately added but only printed between version 0.7 and 0.9.0 to "autopurge" command and API.autopurge, informing they will be renamed "purge"
• in version 0.9.0, API.autopurge and "autopurge" command are renamed "purge", to really reflect what aria2 does. "purge" command might get an "autoremove" alias.

In summary:

• now: deprecation and future change warnings
• v0.7.0: remove API.purge and API.purge_all
• v0.9.0: rename API.autopurge to API.purge and "autopurge" command to "purge" + "autoremove" alias