0.9.2.9000 to 0.9.2 for the pull request.

export update_site, update_site_digests, and prune_site_digests.

fix #340: remove the themesDir field in config.toml by grepping case-insensitively because some themes use the lowercase name themesdir, e.g. https://github.com/vjeantet/hugo-theme-docdock

allow specifying themesDir (instead of theme) via options(); this will make it easier for me to preview the repo yihui/hugo-xmin

add an option to rename file when the date in YAML is updated (I wanted this feature myself for a long time, and finally couldn't stand manually renaming files any more)

fix #312: forgot ! in 6dd9cd52 (should return the YAML as is unless the option blogdown.draft.output is TRUE)

the latest version of yaml can read a character vector of length > 1 now via yaml.load(), and yaml.load_file() can also ignore ---