Support external (i.e. user-defined) trace annotations (#195)

* Support external (i.e. user-defined) trace annotations

- tweaked the python examples to be more balanced
- updated the user-api example to conform to user API changes
- moved the get/set for State and ThreadState to state.{hpp,cpp}
- introduced user-provided trace annotations
- added perfetto python category
- moved coverage impl files around
- created enumerations for mapping category enums to category types
- created enumerations for mapping annotation type enums to annotation values
- moved tracing::add_perfetto_annotations to tracing/annotation.hpp
- utility make_index_sequence_range
- libomnitrace-dl: omnitrace_push_category_region
- libomnitrace-dl: omnitrace_pop_category_region
- libomnitrace-user: omnitrace_user_push_annotated_region
- libomnitrace-user: omnitrace_user_pop_annotated_region
- libpyomnitrace: support extra annotations via annotate_trace config value
  - filename
  - line
  - last attempted instr in bytecode (lasti)
  - argcount
  - num local variables
  - stacksize
- omnitrace-python: -a / --annotate-traces option

* tweak ubuntu-focal workflow

* Fix installation of omnitrace-user headers

* ubuntu-focal-codecov workflow update

- Install texinfo

* Update timemory submodule

examples/python/external.py

@@ -18,7 +18,7 @@ def inefficient(n):
         a += i
         for j in range(n):
             a += j
-    _len = a * n * n * n
+    _len = a * n * n
     _arr = [random.random() for _ in range(_len)]
     _sum = sum(_arr)
     print(f"[{_prefix}] ... sum of {_len} random elements: {_sum}")