Add font input for resume and coverletter

[DeveloperPaul123]

You can now specify the font for the resume and coverletter.

Fixes #50

Example:

#show: coverletter.with(
  author: (
    firstname: "John",
    lastname: "Smith",
    email: "js@gmail.com",
    homepage: "https://example.com",
    phone: "(+1) 111-111-1111",
    github: "DeveloperPaul123",
    linkedin: "John Smith",
    address: "111 Example St. Apt. 111, Example City, EX 11111",
    positions: (
      "Software Engineer",
      "Full Stack Developer",
    ),
  ),
  profile-picture: image("./profile.png"),
  language: "en",
  font: "Times New Roman"
)