Add example of using math() to calculate Haversine Great Circle distance

[krlawrence]

Add to the discussion of Geo Spatial queries that are possible in Gremlin using the examples below that demonstrate calculating the Haversine Great Circle Distance between two airports.

g.withSideEffect("PI", 3.1415926535).
  withSideEffect("rdeg", 0.017453293).
  withSideEffect("gcmiles",3956).        
  V().has('code','AUS').as('src').
  V().has('code','LHR').as('dst').
  select('src','dst').
    by(project('lat','lon').
         by('lat').
         by('lon')).as('grp').
    project('ladiff','lgdiff','lat1','lon1','lat2','lon2').
       by(project('la1','la2').
            by(select('grp').select('src').select('lat')).
            by(select('grp').select('dst').select('lat')).
          math('(la2 - la1) * rdeg')).
       by(project('lg1','lg2').
            by(select('grp').select('src').select('lon')).
            by(select('grp').select('dst').select('lon')).
          math('(lg2 - lg1) * rdeg')).
       by(select('grp').select('src').select('lat')).
       by(select('grp').select('src').select('lon')).
       by(select('grp').select('dst').select('lat')).
       by(select('grp').select('dst').select('lon')).
    math('(sin(ladiff/2))^2 + cos(lat1*rdeg) * cos(lat2*rdeg) * (sin(lgdiff/2))^2').
    math('gcmiles * (2 * asin(sqrt(_)))')              

g.withSideEffect("PI", 3.1415926535).
  withSideEffect("rdeg", 0.017453293).
  withSideEffect("gcmiles",3956).
  V().
  has('code',within('AUS','DFW')).
  group().
    by('code').
    by(project('lat','lon').
      by('lat').
      by('lon')).
  as('grp').
  project('ladiff','lgdiff','lat1','lon1','lat2','lon2').
    by(project('la1','la2').
         by(select('AUS').select('lat')).
         by(select('DFW').select('lat')).
       math('(la2 - la1) * rdeg')).
    by(project('lg1','lg2').
         by(select('AUS').select('lon')).
         by(select('DFW').select('lon')).
       math('(lg2 - lg1) * rdeg')).
    by(select('grp').select('AUS').select('lat')).
    by(select('grp').select('AUS').select('lon')).
    by(select('grp').select('DFW').select('lat')).
    by(select('grp').select('DFW').select('lon')).
    math('(sin(ladiff/2))^2 + cos(lat1*rdeg) * cos(lat2*rdeg) * (sin(lgdiff/2))^2').
    math('gcmiles * (2 * asin(sqrt(_)))')