Use lpeg for parsing snippets

[dcampos]

Problem Statement

Although the current parser gets the job done, having a more powerful and mature library for parsing snippets would be welcome.

Ideas or possible solutions

It seems that lpeg will be included in future releases of Neovim, as this commit seems to indicate.

Alternatives you have considered

Tree-sitter has been considered too, but the required compilation step makes it unappealing. However, it would still be nice to have a tree-sitter grammar for syntax highlighting.