Removing DLPipelines.jl; Learning method -> Learning task

[lorenzoh]

This will incorporate DLPipelines.jl directly into FastAI.jl and drop the dependency. This is a BREAKING change.

In the process, the following changes will be made to the LearningMethod interfaces:

• Rename LearningMethod to LearningTask, method to task
  • In an earlier version of DLPipelines.jl, LearningTask was an abstract parametric type for LearningMethods to signify that there can be multiple ways of solving a task, but this was dropped at some point.
  • LearningTask is imo a more intention-revealing name, as method is a very ambiguous term (especially in Julia-land). This is especially true for the short variable name task vs method.
  • As a result of this, subtypes of LearningMethod will also be renamed. Specifically, [Abstract]BlockMethod -> [Abstract]BlockTask and SupervisedMethod -> SupervisedTask.
  • methoddataset -> taskdataset and methoddataloaders -> taskdataloaders
  • findlearningmethods -> findlearningtasks
• Clean up the basic LearningMethod interface:
  • rename encode(method, ctx, sample) to encodesample. This way, encode is reserved for Encodings.
  • rename decodeŷ to decodeypred . Easier to write and to differentiate from decodey . Old name will be aliased.
• update CHANGELOG