doc: typo fix from javasboy in openresty#27.

doc: bumped version to 0.27 and updated other stuff.

doc: bumped version to 0.26; also stated that we work with nginx 1.5.11.

documented the new feature in srcache_store_skip.

bumped version to 0.24.

updated docs to reflect recent changes.

bumped version to 0.22.

updated docs to reflect recent changes.

updated docs to reflect recent changes; also bumped version to 0.20.

bumped version to 0.19; also added a "Trouble Shooting" section to docs.