Carto metrics

[Algunenano]

Pending testing with static library

cc/ @rafatower

[codecov-io]

Codecov Report

Merging #8 into v3.6.2-carto will decrease coverage by 0.01%.
The diff coverage is 96.15%.

@@               Coverage Diff               @@
##           v3.6.2-carto      #8      +/-   ##
===============================================
- Coverage         96.22%   96.2%   -0.02%     
===============================================
  Files                42      42              
  Lines              8810    8811       +1     
===============================================
  Hits               8477    8477              
- Misses              333     334       +1

Impacted Files	Coverage Δ
src/mapnik_image.hpp	0% <ø> (ø)	⬆️
src/utils.hpp	0% <ø> (ø)	⬆️
src/mapnik_grid.hpp	0% <ø> (ø)	⬆️
src/mapnik_map.cpp	99.92% <100%> (-0.01%)	⬇️
src/node_mapnik.cpp	100% <100%> (ø)	⬆️
src/mapnik_grid.cpp	95.95% <83.33%> (-0.33%)	⬇️
src/mapnik_image.cpp	97.19% <97.22%> (-0.05%)	⬇️

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[Algunenano]

@mtehver Maybe you can have a look at this

Right now I'm getting something like this from Mapnik when requesting pngs (the Mapnik part):

{  
   "authorizedByAPIKey":2,
   "authorize":1,
   "req2params":1,
   "res":7,
   "getTileOrGrid":7,
   "render-png":7,
   "Mapnik":{  
      "Time (us)":568,
      "Calls":1,
      "Setup":{  
         "Time (us)":453,
         "Calls":1,
         "Datasource: Get Features":{  
            "Time (us)":440,
            "Calls":1
         }
      },
      "Render":{  
         "Time (us)":6,
         "Calls":1,
         "Style":{  
            "Time (us)":3,
            "Calls":1,
            "features":0
         }
      }
   },
   "tiles in metatile":1,
   "total":11
}

Any comment about the code or needed measurements (probably in the render part) is welcome.