README.md: formatting improvements

[jiahao]

• Replace 'julia' with 'Julia' in instances where Julia is used as a proper noun
• Reformatted code examples so that they render with GitHub's syntax highlighting
• Cosmetic whitespace changes to code snippets f(x,y,z;w) is now consistently singly spaced after each comma and semicolon, to f(x, y, z; w)
• Minor typos corrected: 'eg' -> 'e.g.', 'proprocessing'
• Replace links to relative URLs where possible, making the documentation consistent across forks and local clones.

Signed-off-by: Jiahao Chen 1732+jiahao@users.noreply.github.com