Gtirb

* Updated "address" iteration order to compare size if addresses are the same
and UUIDs if addresses and sizes are the same so that it can be used to
store objects in ordered containers.
* Fixed some bugs where modifying an object's address or size would cause
findNodeOn to return incorrect results.
* Improved performance of findNodeOn and findNodeAt queries.

* Added module-level endianess flag, for use in archtectures with multiple
possible endians for its code blocks.
* Introduce iteration helpers cfgPredecessors and cfgSuccessors.

* Added a Python wheel to make gtirb-pprinter pip-installable.
* Binary printer always prints against exact library versions.
* Do not remove endbr64 instructions.
* Fix timing issue when running llvm-config in the PE binary printer.
* Add explicit DS register for MASM pprinter.
* Fixup INT1 and INT3 x64 instructions.
* Update the default `--policy` behavior for dynamically linked ELF binaries from `dynamic` to `complete`.
* ARM: Do not rely on `ArchInfo` auxdata.
* ARM: Fail if a CodeBlock cannot be completely disassembled.
* Replace symbolic expression attributes with composable labels.

* Add fixup for rewriting `main` symbol as global.
* Support full paths in `--use-gcc` option.
* Add support for ARM pc-relative `ldr` instruction with register offset.
* Add support for ARM `trap` instructions.
* Emit symbol declarations for symbols attached to `.plt` section.
* Add support for TLSLDM relocationss
* Add detection for `--export-dynamic` in binary printer.

* Remove `--assembler` option; printer now always behaves correctly when
escaping characters.
* Support generating ELF symbol version information in assembly output.
* Add `--version-script` argument for generating ELF version scripts.
* Removed explicit transformations to GTIRB from PrettyPrinter. Clients
will now need to explicitly opt in to these transforms. `gtirb-pprinter`
behavior is unchanged.

* Fix bugs in printing shift instructions in AT&T syntax.
* Add `--use-gcc` option overriding `gcc` executable when binary printing ELF files.
* Fix printing symbols with a displacement of zero in ARM64 indirect operands.
* Expand `--help` message by listing options for `--isa`, `--syntax`, `--assembler`, and `--policy`.
* Fix bug resulting in skipped `.data` sections.
* Ubuntu 18 and gcc 7 are no longer supported.
* Default syntax in `assembler` mode changed to AT&T (i.e., `att`).