Per @steveklabnik's comment [here](https://github.com/rust-lang/cargo/issues/739#issuecomment-130085860), the Pandoc components of the Makefile are no longer used, and as such the corresponding components of the documentation are out of date.
- I've removed the Pandoc (and therefore also LaTeX) elements of the makefile and confirmed that the build proceeds correctly.
- I updated the documentation to reference `rustdoc` and of Pandoc.
r? @steveklabnik
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