TAJO-1069: TAJO-1069: Add document to explain High Availability support. (jaehwa)

Closes #180
TAJO-1105: Add thread which detects JVM pauses like HADOOP's. (jinho)

Closes #191
TAJO-1107: Broadcast join on non-leaf node scans only first data file.

Closes #193
TAJO-1110: JAVA_PULLSERVER_HEAP_MAX in bin/tajo should be increased.

Closes #197