geographic axes for Kyrix-S

[tracyhenry]

This PR allows specification of geo axes, freeing the user from manually transforming lat/lon to screen coordinates.

now you can specify the following:

ssv = {
...
layout: {
  x:{
    field: 'latitude'
  },
  y:{
    field: 'longitude'
  },
  geo:{
    level: 5,
    center: [39.5, -98.5]
  }
},
...
}

the initial viewport will be pointed to layout.geo.center at zoom level layout.geo.level. And an OpenStreet map background will be automatic rendered.

[asah]

Nice!

[asah]

Add comment explaining REPLACE_ME ?

[asah]

SQL injection...

suggestion: instead of using injection safe parameters (ugly pain), rename getRawTable() to add something indicating safety e.g. getRawTableSqlSafe(), and then inside the function, restrict the character set to ensure no injection, I.e. you don't care about during weird table names. Wrapping also works (e.g. sqlSafe(getRawTable()) though it requires told support to ensure that you don't forget to do this everywhere...

[tracyhenry]

Makes sense. Since getRawTable returns a table name we get from compiler - the validation should be done in compiler.

I think this falls into the bigger issue #15, where we need to do better validation of user spec to deal with "overly clever" developers.