Add render-based test for the oup_article pre_knit hook (#603)

The direct `fmt$pre_knit(...)` unit test verifies the warning logic but
not that rmarkdown actually invokes the hook with the parsed YAML
metadata. Add a knit-only render (run_pandoc = FALSE) of an Rmd whose
YAML sets `authormark`, asserting the warning surfaces — covers the
hook-wiring contract regardless of rmarkdown internals.

Skips when pandoc <2.10 (the format already requires it).

Do bibliography commands logic in R instead of doing in TeX

The convoluted logic using \ifboolexpr and \ifstrequal in the preamble of
template.tex is done now done in function tf_article(). A new pandoc
variable ("biblio-commands") is now used.

version 0.27

Update to version 0.26

Bump version

Release 0.24

release rticles 0.23

Bump version

CRAN release v0.21

CRAN release v0.20