Separate compilation and linker phases (#376)

Separate between compilation and linker phases to allow deploy time
linking and back-porting era compiler changes to fix #91. Unlinked
contract binaries (caused by missing libraries or missing factory
dependencies in turn) are emitted as raw ELF object.

Few drive by fixes:
- #98
- A compiler panic on missing libraries definitions.
- Fixes some incosistent type forwarding in JSON output (empty string
vs. null object).
- Remove the unused fallback for size optimization setting.
- Remove the broken `--lvm-ir`  mode.
- CI workflow fixes.

---------

Signed-off-by: Cyrill Leutwiler <bigcyrill@hotmail.com>
Signed-off-by: xermicus <bigcyrill@hotmail.com>
Signed-off-by: xermicus <cyrill@parity.io>

crates/yul/src/lexer/mod.rs

@@ -1,8 +1,5 @@
 //! The compiler lexer.
 
-pub mod error;
-pub mod token;
-
 #[cfg(test)]
 mod tests;
 
@@ -16,6 +13,9 @@ use self::token::lexeme::Lexeme;
 use self::token::location::Location;
 use self::token::Token;
 
+pub mod error;
+pub mod token;
+
 /// The compiler lexer.
 pub struct Lexer {
     /// The input source code.