Duration Rename

- In preparation for a new (different) Duration object, the source files need
  to be renamed.
Unit Tests

- The cal.t tests use an abbreviated 'cal' command, which is no longer unique
  given the new 'calc' command.
Copyright

- Updated (visible) copyright to 2014.
RX

- Merged libexpr changes.
UTF8

- Merged libexpr changes.
Nibbler

- Merged libexpr changes.
ISO8601

- Merged libexpr ISO8601 code.
Unit Tests

- Renamed duration.t.cpp to old_duration.t.cpp, ready for the new duration
  tests.
Lexer, Duration

- Merged libexpr code.
Duration

- Renamed Duration object to OldDuration so that the two implementations can
  coexist in a binary.
Unit Tests

- Added libexpr Duration unit tests.
Unit Tests

- Merged libexpr Lexer tests.
- Updated .gitignore.
Variant

- Merged libexpr changes.
Unit Tests

- Merged libexpr Variant tests.
- Updated .gitignore.
Dates

- Merged libexpr Dates support.
Eval

- Merged libexpr Eval support.
Unit Tests

- Merged libexpr eval tests.
Calculator

- Added standalone calculator utility.
Unit Tests

- Added calculator tests.
Unit Tests

- Added calculator bug unit tests.