Flag: markdown-*-content

[hjr3]

This issue is part of #125

I'm lumping two into this issue:

--markdown-before-content: include more markdown before the content

Using this flag looks like this:

$ rustdoc src/lib.rs --markdown-before-content extra.md
$ rustdoc README.md --markdown-before-content extra.md

This flag takes a list of files, and inserts them inside the tag but
before the other content rustodc would normally produce in the rendered
documentation.

--markdown-after-content: include more markdown after the content

Using this flag looks like this:

$ rustdoc src/lib.rs --markdown-after-content extra.md
$ rustdoc README.md --markdown-after-content extra.md

This flag takes a list of files, and inserts them inside the tag but
after the other content rustdoc would normally produce in the rendered
documentation.

---

Should we keep these flags or not?

[hjr3]

@steveklabnik I noticed these two flags were missing. The triage is probably the same as #145 but I wanted to be thorough.

[steveklabnik]

Yeah, thanks! It is.