API for adornments

[Ducasse]

figures, math equations and a code block can offers a caption.
We should be able to access these in a polymorphic way.

See the code of the MicLastPeriodInCaptionChecker class.

Here is a test for such functionality

generateFilesystemExample

	| file |
	file := fileSystem workingDirectory / 'codeCaptionMissingPeriod.md'.
	file writeStreamDo: [ :stream |
			stream nextPutAll: '

```caption=This is the famous missing period
setX: xInt setY: yInt

	...
```' ].

	file := fileSystem workingDirectory / 'figureCaptionMissingPeriod.md'.
	file writeStreamDo: [ :stream |
			stream nextPutAll: '

![This is the famous missing period](figures/f.png)
' ].

	file := fileSystem workingDirectory / 'equationCaptionMissingPeriod.md'.
	file writeStreamDo: [ :stream |
			stream nextPutAll: '
$$%caption=This is the famous missing period
\frac{1}{2}
$$
].
' ].

	file := fileSystem workingDirectory / 'codeCaptionEndingWithPeriod.md'.
	file writeStreamDo: [ :stream |
			stream nextPutAll: '

```caption=This is the famous correctly ending period.
setX: xInt setY: yInt

	...
```' ].

	file := fileSystem workingDirectory / 'figureCaptionEndingWithPeriod.md'.
	file writeStreamDo: [ :stream |
			stream nextPutAll: '

![This is the famous correctly ending period.](figures/f.png)
' ].

	file := fileSystem workingDirectory / 'equationCaptionEndingWithPeriod.md'.
	file writeStreamDo: [ :stream |
			stream nextPutAll: '
$$%caption=This is the famous correctly ending period.
\frac{1}{2}
$$
].
' ]