Add a few references to the FE_Q_iso_Q1 element documentation.

[bangerth]

No description provided.

[bangerth]

/rebuild

[kronbichler]

Looks good, thank you for the references. I added just a small comment below.

[kronbichler]

Can we rename this into

Suggested change

	@article{taho73,
	@article{Taylor73,

to give those people who do not want to click the reference an idea what the paper is about? (I do not like to click on reference links and just look at the name of the web page linked to, which picks up this reference and thus I like expressive names for the papers.)

[bangerth]

So changed! :-)

[kronbichler]

Thanks!

[bangerth]

I tend to think that we ought to have more references to the literature, and this one was a fun find while working on a project in which the Taylor-Hood element was important.