Deprecated APIs for Task Registration

[Anjiang-Wei]

I am now trying to make a second pass over the Legion manual while reading the source code of legion.h

I found two issues with the current manual:

• Deprecated task registration API
  tasks.tex mentions the API register_legion_task
  tasks.tex mentions "two boolean flags".
  As indicated in legion.h, register_legion_task is a deprecated API for task registration.

• Dynamic task registration should now be supported
  tasks.tex mentions
  Every task and its task id must be registered with the high level runtime. Currently all tasks must be registered before the runtime starts.

Please refer to the new APIs: preregister_task_variant and register_task_variant
Legion now supports dynamic task registration, and it is allowed to provide user data to associate with the task variant.

Minor issues:

• tasks.tex:
  tasks arguments should be task arguments
• tasks.tex:
  a different address space than the caller: than should be from

[lightsighter]

If you compile the examples with c++14 or later the compiler should tell you about the use of any deprecated APIs.