add dispose cb to refcounting alloc
use refcount for mimemaps, and make it part of file.c
add tests (and fix a bug) in the refactored mimemap impl.
implement h2o_mimemap_remove_type
refactor the mime-type configuration directives to: file.mime.(settypes|addtypes|removetypes)
add a tiny hard-coded mimemap, refer to the results in the unit tests of file.c
`paths` should be a mandatory element of `hosts`
Merge branch 'master' into kazuho/expr/mime-types-as-part-of-file
add end-to-end tests for mime-type configuration
add confvar `file.mime.setdefaultype` and tests
ease the configuration of the file handler by making the arguments optional
update the examples
Merge branch 'kazuho/expr/mime-types-as-part-of-file'