Create a glossary of key terms

[DimmestP]

Inspired by stan's LOO glossary https://github.com/stan-dev/loo/blob/master/R/loo-glossary.R

From #85 Flic's code review

or calculate_deltacq_bysampleid(): maybe explain what 'delta cq' means? or refer to where you've explained this in the package? I found it tricky to identify what 'cq' stands for? The delta means a 'change in', doesn't it? Is 'cq' related to 'quantification cycle'? Maybe users would know this stuff already, but for new users/inexperienced researchers it'd be handy to have a glossary/link to a resource with more details?

[ewallace]

That is a very nice idea.