Usage:
https://gravatar.williamli.dev/
-> my default gravatar @ 512px
https://gravatar.williamli.dev/{size}
-> my default gravatar @ {size}px
https://gravatar.williamli.dev/email/{email}
-> gravatar of {email} @ 512px
https://gravatar.williamli.dev/email/{email}/{size}
-> gravatar of {email} @ {size}px
https://gravatar.williamli.dev/h/{email hash}
-> gravatar of {email hash} @ 512px
https://gravatar.williamli.dev/h/{email hash}/{size}
-> gravatar of {email hash} @ {size}px