Handling period durations of days with `T` prefix (#74)

* Added `fixInvalidDayOffset`

Signed-off-by: Arnau Mora <arnyminer.z@gmail.com>

* Added tests for `fixInvalidDayOffset`

Signed-off-by: Arnau Mora <arnyminer.z@gmail.com>

* Implemented `fixInvalidDayOffset`

Signed-off-by: Arnau Mora <arnyminer.z@gmail.com>

* Added `testFixInvalidDuration`

Signed-off-by: Arnau Mora <arnyminer.z@gmail.com>

* Comments

Signed-off-by: Arnau Mora <arnyminer.z@gmail.com>

* Generalize stream preprocessors

* Using `regexpForProblem` instead of `INVALID_DAY_PERIOD_REGEX`

Signed-off-by: Arnau Mora <arnyminer.z@gmail.com>

* Clean fixme

Signed-off-by: Arnau Mora <arnyminer.z@gmail.com>

* Added `FixInvalidDayOffsetPreprocessorTest`

Signed-off-by: Arnau Mora <arnyminer.z@gmail.com>

* Typo

Signed-off-by: Arnau Mora <arnyminer.z@gmail.com>

* Fixed tests

Signed-off-by: Arnau Mora <arnyminer.z@gmail.com>

* Moved test to `FixInvalidDayOffsetPreprocessorTest`

Signed-off-by: Arnau Mora <arnyminer.z@gmail.com>

* Changed conversion to `PT`-`P`

Signed-off-by: Arnau Mora <arnyminer.z@gmail.com>

* Updated tests

Signed-off-by: Arnau Mora <arnyminer.z@gmail.com>

* Minor changes

Signed-off-by: Arnau Mora <arnyminer.z@gmail.com>
Co-authored-by: Ricki Hirner <hirner@bitfire.at>