Config template: add boto_calling_format S3 option

Using the "ordinary" calling format can be useful when using
a bucket whose name contains periods (otherwise the AWS SSL
certificate may be refused because it is several subdomains
deep).
Merge pull request #625 from krallin/aws-calling-format

Config template: add boto_calling_format S3 option
Correcting typos in the {ADVANCED, CONTRIBUTING, README}.md files.
Merge pull request #628 from krook/fix-markdown-typoes

Correcting typos in the {ADVANCED, CONTRIBUTING, README}.md files.