Display correct line numbers for multiple .text sections (#63)

* Support multiple DWARF sequences

* Rework DWARF line info parsing

- Properly handles multiple sections
  in DWARF 1
- line_info moved into ObjSection
- DWARF 2 parser no longer errors with
  no .text section
- Both parsers properly skip empty
  sections

* Simplify line_info (no Option)

---------

Co-authored-by: Luke Street <luke.street@encounterpc.com>

objdiff-core/src/arch/mips.rs

@@ -112,10 +112,7 @@ impl ObjArch for ObjArchMips {
                     }
                 }
             }
-            let line = obj
-                .line_info
-                .as_ref()
-                .and_then(|map| map.range(..=cur_addr as u64).last().map(|(_, &b)| b));
+            let line = section.line_info.range(..=cur_addr as u64).last().map(|(_, &b)| b);
             insts.push(ObjIns {
                 address: cur_addr as u64,
                 size: 4,