Merge pull request #1597 from golang/updatedesc

all: update descriptor.proto to latest version

Merge pull request #1363 from neild/jsonnull

jsonpb: accept 'null' as a valid representation of NullValue in unmarshal

all: deprecate the module (#1306)

Use the new deprecation feature to mark this module as deprecated.
See https://golang.org/issue/40357.

Considerations:
* google.golang.org/protobuf/cmd/protoc-gen-go@v1.25.0 and below
used to generate a hard dependency on github.com/golang/protobuf,
which would be frustrating since it would force an explicit dependency
on a deprecated module. However, that is no longer the case in v1.26.0.
* google.golang.org/protobuf and github.com/golang/protobuf have
a cyclic dependency on each other. However, this should not be a problem
since proposal 40357 only marks direct dependencies in the go.mod file,
rather than all transitive dependencies in the go.sum file.

all: depend on google.golang.org/protobuf@v1.26.0 (#1293)

all: depend on google.golang.org/protobuf@v1.26.0-rc.1 (#1292)

jsonpb: Fix marshaling of Duration (#1221)

Negative nanosecond should not have negative sign after decimal point.
Add check for max and min seconds.

Fixes #1219.

all: upgrade to google.golang.org/protobuf@v1.23.0 (#1131)

all: upgrade to google.golang.org/protobuf@v1.22.0 (#1114)

all: upgrade to google.golang.org/protobuf@v1.21.0 (#1081)

go.mod: set go version to go1.9 (#1055)