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/common/src/lib.rs

@@ -3,9 +3,13 @@
 pub(crate) mod base;
 pub(crate) mod bit_length;
 pub(crate) mod byte_length;
+pub(crate) mod contract_identifier;
 pub(crate) mod evm_version;
 pub(crate) mod exit_code;
 pub(crate) mod extension;
+pub(crate) mod keccak256;
+pub(crate) mod metadata;
+pub(crate) mod object;
 pub(crate) mod utils;
 
 pub use self::base::*;
@@ -14,4 +18,8 @@ pub use self::byte_length::*;
 pub use self::evm_version::EVMVersion;
 pub use self::exit_code::*;
 pub use self::extension::*;
+pub use self::keccak256::*;
+pub use self::metadata::*;
+pub use self::object::*;
 pub use self::utils::*;
+pub use contract_identifier::*;