File Format

- File format 2 (used in version 0.9.3 - 1.5.0) is no longer supported.
- Task::parseJSON implemented.
- PRODUCT_TASKWARRIOR defined, to facilitate code sharing.
- Strings renamed for sharing purposes.
Import

- The import command now uses the built-in Task::parseJSON method.
- Began t3.t.cpp for JSON parsing tests.
Unit Tests

- Added a non-trivial JSON task to parse.
Shared Code

- Added '#ifdef PRODUCT_TASKWARRIOR' in enough places that taskd can now share an
  identical copy of Task.{h,cpp}.
Performance Testing

- Added import and export to the testing.  As an extension mechanism, it needs
  to perform well.