Disambiguate 'target' anchors in slangc reference

[AndrewBrownK]

There is a misleading/confusing link in the slangc reference when read on GitHub (here).

There are a few different links/anchors identified as "target" (try case insensitive search id="target while editing the file). One of these sections talks about the -target option itself (id="target-1"). Another section talks about other options related to target code generation (id="Target" with capital T). The last lists the specific values that you can feed to the -target option (id="target" with lowercase t).

This might work as intended in some markdown viewers/editors (I don't know). However, GitHub converts the element IDs to lowercase and so two of these links are ambiguous. Thus when reading this documentation and seeking valid options for -target, clicking the link to find those options leads to the wrong section.

In this PR I have changed the title and id of Target to Target Options, so now each target related hyperlink works as intended. This can be tested on my branch here. I cannot attest/confirm that this is bug free in other markdown viewers/editors.

I'm not sure why GitHub is showing this diff is a binary file/change.

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[csyonghe]

This markdown file is generated by running slangc so we need to fix the docgen logic in the compiler code instead of fixing directly the md file.

Should change source\slang\slang-options.cpp L114.