Emit references for function templates

[Varun Gandhi]

• Standalone function templates #291
• Function declarations inside function templates? I noticed this comment which seems these require special care:

    /// Specify that this function declaration was instantiated from a
    /// FunctionDecl FD. This is only used if this is a function declaration
    /// declared locally inside of a function template.
    void setInstantiatedFromDecl(FunctionDecl *FD);

Based on the test added in #287 -- references to non-method function templates are just not working. 😱

[Varun Gandhi]

The second part doesn't seem to be relevant here. I'm going to file a separate issue #293