Update API URLs to match linode-docs-theme#400

[nmelehan]

The following sed command will perform the required search-and-replace on a given markdown file in the docs repo:

's/\(\/docs\/api\/[a-z-]*\)\/#\([a-z-]*\)/\1\/\2\//g'

This command can be run on Linux (probably not on macOS without some tweaking) to execute the search and replace on all markdown files in the docs repo:

find ./ -type f -name '*.md' -exec sed -i -e 's/\(\/docs\/api\/[a-z-]*\)\/#\([a-z-]*\)/\1\/\2\//g' {} \;