resolc crate (#328)

- Factor the YUL crate out of `revive-solidity`.
- `revive-solidity` is in reality not a Solidity implementation but the
revive solidity compiler driver (`resolc`). By renaming we not only get
this straight but also a binary with the same name as the crate which
should be less confusing.

---------

Signed-off-by: Cyrill Leutwiler <bigcyrill@hotmail.com>

crates/yul/src/parser/mod.rs

@@ -0,0 +1,18 @@
+//! The YUL code block.
+
+pub mod error;
+pub mod identifier;
+pub mod statement;
+pub mod r#type;
+
+use crate::lexer::error::Error as LexerError;
+use crate::lexer::token::Token;
+use crate::lexer::Lexer;
+
+/// Returns the `token` value if it is `Some(_)`, otherwise takes the next token from the `stream`.
+pub fn take_or_next(mut token: Option<Token>, lexer: &mut Lexer) -> Result<Token, LexerError> {
+    match token.take() {
+        Some(token) => Ok(token),
+        None => lexer.next(),
+    }
+}