Condition final line item macros based on YAML

[coatless]

Condition these final three lines:

• Show Acknowledgements
• Show Materials
• Show references

c.f.

pinp/inst/rmarkdown/templates/pdf/resources/template.tex

Lines 74 to 76 in b6bf4c9

	\showmatmethods
	\showacknow
	\pnasbreak

The hope here is these will address the fragile state of the floats...

[eddelbuettel]

We may actually just kill showmatmethods which we don't support in the header.

Another one that would be nice is to not auto-insert the bibliography so that when a user is in a fight with latex over floats, it may give a chance to do bibliographies manually.