tex-tcolorbox{,-doc}: update to 6.0.3

6.0.0
### Added
- Generalized text alignment options (issue #184)
    - Option `halign code`
    - Option `halign upper code`
    - Option `halign lower code`
    - Option `halign title code`
- New Options:
    - Option `before title*` (equals `before title` until 5.1.1)
    - Option `after title*`  (equals `after title` until 5.1.1)
- New option for verbatim output and listings:
    - Option `verbatim ignore indention at end`
- Option `short title` (part of issue #186)
- Support for zref / zref-titleref / zref-clever (issue #206)
    - Option `label is label`
    - Option `label is zlabel`
- Library `theorems`: New theorem generation macros. Generated theorema
    support an optional short title now (part of issue #186):
    - `\NewTcbTheorem`
    - `\RenewTcbTheorem`
    - `\ProvideTcbTheorem`
    - `\DeclareTcbTheorem`
- Library `skins`: Default values added to the options
    - `watermark zoom`
    - `watermark shrink`
    - `watermark overzoom`
    - `watermark stretch`

- The 'TikZ Image and Picture Fill Extensions' are extracted from library `skins`
    into an `tcolorbox` indendent TikZ library `tikzfill.image` and made part
    of a new package `tikzfill`. Also, the respective documentation is moved into
    this new package (issue #185)
- Library `skins`: The implementation of all watermark options is changed and
    adapted to `tikzfill`. `clip watermark=false` has now some restrictions
- Library `skins`: `\tcbincludegraphics` implementation changed to LaTeX3 code

6.0.1
- Typo in CHANGES.md
- Regression bug: `\NewTCBInputListing` without initialization
  options produces an error

6.0.3
### Added
- Usage of `\tcblower` where not applicable gives a more helpful error message
- Usage of `capture=fitbox` for `\tcbox` gives an error message
- Library documentation:
    - Macro `\sarg`

### Changed
- Documentation:
    - List of initialization option macros enlarged
    - Removed `xparse` references
    - Typo correction
- Library `skins`:
    - `\tcbhypernode` made compatible for xelatex

### Fixed
- `parbox=false` accumulated negative `\parskip` values, if called several times
    or used with `attach title to upper`
- Library `breakable`:
    - Reverting to `\color{.}` hack to avoid color bleeding after the box
    - `Discard zero height first box part` problem hopefully solved

(markd)