Make StringTable public (#16)

I missed this when pushing the commit, StringTable should be
pub so that the desired functionality of "get your own String
Table and change the address" can work.

src/lib.rs

@@ -2,7 +2,7 @@
 
 use header::{Tag, TagIter};
 pub use boot_loader_name::BootLoaderNameTag;
-pub use elf_sections::{ElfSectionsTag, ElfSection, ElfSectionIter, ElfSectionType, ElfSectionFlags};
+pub use elf_sections::{ElfSectionsTag, ElfSection, ElfSectionIter, ElfSectionType, ElfSectionFlags, StringTable};
 pub use elf_sections::{ELF_SECTION_WRITABLE, ELF_SECTION_ALLOCATED, ELF_SECTION_EXECUTABLE};
 pub use memory_map::{MemoryMapTag, MemoryArea, MemoryAreaIter};
 pub use module::{ModuleTag, ModuleIter};