Add additional units to EXTRACT, DATE_PART, TRUNC for temporal data types

For EXTRACT, DATE_PART, add:

• week
• dow (day of week)
• doy (day of year)
• seconds (to complment second)
• microsecond / microseconds
• nanosecond / nanoseconds

For TRUNC add:

• SS (seconds)

For less than seconds truncation, use DATE_TRUNC() IMPALA-5317 since there is no standard for abbrievations less than SS (seconds) per Vertica

References:

• https://www.postgresql.org/docs/current/static/functions-datetime.html
• https://my.vertica.com/docs/8.1.x/HTML/index.htm#Authoring/SQLReferenceManual/Functions/Date-Time/EXTRACT.htm
• https://www.ibm.com/support/knowledgecenter/en/SSULQD_7.1.0/com.ibm.nz.dbu.doc/r_dbuser_functions_expressions_extract_datetime.html
• http://docs.aws.amazon.com/redshift/latest/dg/r_Dateparts_for_datetime_functions.html