Support operations Like FieldName[2].key == SomeValue

[NathanSpeidel]

Currently values in a map can be accessed via

FieldName.key

Add support for accessing elements in a list as well:

FieldName[2].key

[akshaisarma]

I think we should use our existing syntax such as FieldName.0.key and when we access FieldName, we know its type (List or Map). If it's a List, then we use the next accessor as an index into the List, otherwise, we treat it as a String index into a Map.

[akshaisarma]

Addressed Filters and Aggregations with #68. Projections require more help from bullet-record