Remove ineffective else clauses (google#464)

Unify overflow checking in operators, field setting (google#448)

* Unify overflow checking in operators, field setting
* Additional overflow case for timestamp subtraction
* NaN checks and tests based on review feedback

Fix infinite loop in AST prune (google#419)

Ensure that proto reflection falls back to dynamic lookup (google#413)

* Ensure that proto reflection falls back to dynamic lookup when the descriptors are not shared by CEL and the proto
* Fix the BUILD.bazel rules

Ensure protodesc.FileDescriptor references are sourced from the globa…

…l proto registry when possible (google#411)

Switch from Travis to Google Cloud Build (google#406)

Use custom build image with timezone fix. (google#391)

Add runtime support for timestamp from Unix epoch (google#358)

Introduce a sync.Pool for ANTLR Lexer / Parser instances (google#348)

* Introduce a sync.Pool for ANTLR Parser instances
* Introduce sync.Pool instances for the Lexer as well.

Note, the change brings in github.com/antlr/antlr4/pulls/2816 which updates the
ANTLR Go runtime. Other applications using vendored code, or alternate sources
of truth besides the main ANTLR GitHub repository will also need to be udpated
for this change to work.

Spelling, simplification, and effective if improvements (google#339)