Minor Javadoc fixes

[dhalperi]

• Add package-info.java to two missing packages.
• Fix a compile error leftover from changing a link to a code block,
  which requires dropping HTML escaping of brackets.

R @davorbonaci

[davorbonaci]

Travis error seems unrelated. @mxm, any thoughts? I'll retry the test.

-------------------------------------------------------
 T E S T S
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Running org.apache.beam.runners.flink.streaming.GroupByNullKeyTest
#
# A fatal error has been detected by the Java Runtime Environment:
#
#  SIGBUS (0x7) at pc=0x00007f0dffbe97d2, pid=5132, tid=139698220291840
#
# JRE version: Java(TM) SE Runtime Environment (8.0_31-b13) (build 1.8.0_31-b13)
# Java VM: Java HotSpot(TM) 64-Bit Server VM (25.31-b07 mixed mode linux-amd64 compressed oops)
# Problematic frame:
# C  [libzip.so+0x117d2]  newEntry+0x62
#
# Failed to write core dump. Core dumps have been disabled. To enable core dumping, try "ulimit -c unlimited" before starting Java again
#
# An error report file with more information is saved as:
# /home/travis/build/apache/incubator-beam/hs_err_pid5132.log
Compiled method (nm)  271177  115     n 0       java.util.zip.ZipFile::getEntry (native)
 total in heap  [0x00007f0df0f53050,0x00007f0df0f533c0] = 880
 relocation     [0x00007f0df0f53178,0x00007f0df0f531c0] = 72
 main code      [0x00007f0df0f531c0,0x00007f0df0f533c0] = 512
#
# If you would like to submit a bug report, please visit:
#   http://bugreport.java.com/bugreport/crash.jsp
# The crash happened outside the Java Virtual Machine in native code.
# See problematic frame for where to report the bug.
#
/home/travis/build.sh: line 172:  5132 Aborted                 (core dumped) "$@"
The command "mvn -B -DforkCount=0 install -U" failed 3 times.

LGTM otherwise.

[mxm]

@davorbonaci Never seen this one before. The error occurs in java.util.zip.ZipFile::getEntry, so probably while accessing a corrupted class file inside a Jar. Or maybe disk space full. Looks like a Travis related problem.

PR looks good!