Enhancers: Temporal extent enhancer

[izaslavsky]

Parse text to figure out the actual date of measurements, or extent (eventually will be done via introspection). For now, may decide if citation date should be used as temporal extent

[valentinedwv]

I don't think citation date as temporal always applies, although for indexing we could have it be the fallback.

[izaslavsky]

Steps:

• identify files with no temporal extent, that have some time identifier
• extract title and abstract
• use an NLP system to see if it can identify time keywords. How to ID terms and time
  ** if NLP does not work, then mark up and machine learning?
• convert to time

Improvements

• time range identification.
• identify before, after, prior as keywords for time and geologic terms
• validating time extent by what is in abstract vs what is listed in metadata time extent