Docsp 9586 (#84)

* begin converting existing md to rst

* aggregates builders

wip

agg builders

copy agg builders

change otp depth

remove empty heading

change heading level

depth

headings

sort out errors

headings

grammar

* cleanup

* broken links

* nits

* add missing field

* nits

* link to projection page

* doc link

* correct wording for out stage

Author: terakilobyte

.gitignore

@@ -24,6 +24,7 @@ hs_err_pid*
 
 # authoring workspace files
 .vscode*
+.idea
 build/
 *pyc
 .DS_Store

source/fundamentals/aggregation.txt

@@ -13,6 +13,8 @@ Aggregation
 Overview
 --------
 
+.. _java-aggregation:
+
 Aggregation operations process data in your MongoDB collections and return computed results. MongoDB's Aggregation
 framework is modeled on the concept of data processing pipelines. Documents enter a multi-staged pipeline that
 transforms the documents into an aggregated result.