Add support for CMakeTest tests and sections

[AutonomicPerfectionist]

This pull request adds new processors to recognize documented tests and sections. Additionally, it fixes a previously unknown bug where indented docs would not be processed correctly.

[ryanmrichard]

This looks like it works for the particular use case in #34; feel free to ignore my .. function suggestion. We can revisit that later if someone wants to separate documentation from the thing being documented.

[dschiller]

Seems there is some debug output left:

Writing RST files to /Users/dirk.schiller/Work/Coding/CPP/cmake-tools-tests/docs/docs
ANTLR runtime and generated code versions disagree: 4.8!=4.7.2
ANTLR runtime and generated code versions disagree: 4.8!=4.7.2
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# Testing ``buildserver_helper.cmake``
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# Verify the global option ``BUILDSERVER`` defaults to ``OFF``
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# Verify the global option ``RELEASEBUILD`` defaults to ``OFF``
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# Verify variable ``BUILDNUMBER`` defaults to ``0`` ( Zero )
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# Verify variable ``VERSION`` defaults empty
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# Verify variable ``BUILD_ID`` defaults empty
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# Verify variable ``FULL_VERSION`` defaults to empty
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# Testing macro ``private_buildnumber_commons``
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# Verify ``IsStableBuild`` is ``1`` if ``RELEASEBUILD`` is ``ON``
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# Verify ``IsStableBuild`` is ``0`` if ``RELEASEBUILD`` is ``OFF``
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# Verify ``FULL_VERSION`` is ``VERSION`` if ``FULL_VERSIOM`` is not set
Writing for file /Users/dirk.schiller/Work/Coding/CPP/cmake-tools-tests/cmakelibs/tests/buildserver-helper.cmake
Writing RST file /Users/dirk.schiller/Work/Coding/CPP/cmake-tools-tests/docs/docs/buildserver-helper.rst
ANTLR runtime and generated code versions disagree: 4.8!=4.7.2
ANTLR runtime and generated code versions disagree: 4.8!=4.7.2
Writing for file /Users/dirk.schiller/Work/Coding/CPP/cmake-tools-tests/cmakelibs/tests/bundle-helper.cmake
Writing RST file /Users/dirk.schiller/Work/Coding/CPP/cmake-tools-tests/docs/docs/bundle-helper.rst
Running Sphinx v3.4.3
loading pickled environment... done
building [mo]: targets for 0 po files that are out of date
building [html]: targets for 3 source files that are out of date
updating environment: 0 added, 3 changed, 0 removed
reading sources... [100%] docs/bundle-helper                                                                                                                                                                                               
looking for now-outdated files... none found
pickling environment... done
checking consistency... done
preparing documents... done
writing output... [100%] index                                                                                                                                                                                                                
generating indices... genindex py-modindex done
writing additional pages... search done
copying static files... done
copying extra files... done
dumping search index in English (code: en)... done
dumping object inventory... done
build succeeded.

[AutonomicPerfectionist]

Debug output removed in #36