Update README to comply with Markdown Lint

[santiagofn]

Changes were made according to https://github.com/DavidAnson/markdownlint

They include:

• Make all unordered list use asterisks
• Add empty lines before/after lists and code blocks
• Add language ref to code blocks
• Replace <code> with backticks
• Fix wrong link refs

[santiagofn]

@reosarevok @yvanzo thanks for your feedback! I've added 3 more commits: the first 2 fix things you mentioned and the last one enforces a max line length (most of the text complied with that but there were fragments that didn't; I also added an exception for code blocks).

Let me know what you think about it and if I need to make more amends!

PS: I didn't know if you ask contributors to respect certain style on commit messages, like e.g. using a prefix, or if I must rebase all the commits into an unique commit. Let me know about that too!