Elixir agents/maps, Ruby conventions/docs (#2116)

* Add name to contributors list

* Fix typo

* Note convention on curly-braced blocks

* Replace hardcoded link to 2.1.1 documentation with generic current link

* Add notes on Elixir agents

* Add explanation of maps

* Add name to contributors list

* Fix code fence that was obscuring markdown

* Fix syntax error

* Remove disputed comment

* Remove from contributors list

elixir.html.markdown

@@ -3,6 +3,7 @@ language: elixir
 contributors:
     - ["Joao Marques", "http://github.com/mrshankly"]
     - ["Dzianis Dashkevich", "https://github.com/dskecse"]
+    - ["Ryan Plant", "https://github.com/ryanplant-au"]
 filename: learnelixir.ex
 ---
 
@@ -96,6 +97,14 @@ string.
 lower..upper = 1..10 # Can use pattern matching on ranges as well
 [lower, upper] #=> [1, 10]
 
+# Maps are key-value pairs
+genders = %{"david" => "male", "gillian" => "female"}
+genders["david"] #=> "male"
+
+# Maps with atom keys can be used like this
+genders = %{david: "male", gillian: "female"}
+genders.gillian #=> "female"
+
 ## ---------------------------
 ## -- Operators
 ## ---------------------------
@@ -407,6 +416,23 @@ send pid, {:circle, 2}
 
 # The shell is also a process, you can use `self` to get the current pid
 self() #=> #PID<0.27.0>
+
+## ---------------------------
+## -- Agents
+## ---------------------------
+
+# An agent is a process that keeps track of some changing value
+
+# Create an agent with `Agent.start_link`, passing in a function
+# The initial state of the agent will be whatever that function returns
+{ok, my_agent} = Agent.start_link(fn -> ["red, green"] end)
+
+# `Agent.get` takes an agent name and a `fn` that gets passed the current state
+# Whatever that `fn` returns is what you'll get back
+Agent.get(my_agent, fn colors -> colors end) #=> ["red, "green"]
+
+# Update the agent's state the same way
+Agent.update(my_agent, fn colors -> ["blue" | colors] end)
 ```
 
 ## References

ruby.html.markdown

@@ -210,7 +210,7 @@ array.push(6) #=> [1, 2, 3, 4, 5, 6]
 # Check if an item exists in an array
 array.include?(1) #=> true
 
-# Hashes are Ruby's primary dictionary with keys/value pairs.
+# Hashes are Ruby's primary dictionary with key/value pairs.
 # Hashes are denoted with curly braces:
 hash = { 'color' => 'green', 'number' => 5 }
 
@@ -612,7 +612,7 @@ Something.new.qux # => 'qux'
 
 - [Learn Ruby by Example with Challenges](http://www.learneroo.com/modules/61/nodes/338) - A variant of this reference with in-browser challenges.
 - [An Interactive Tutorial for Ruby](https://rubymonk.com/) - Learn Ruby through a series of interactive tutorials.
-- [Official Documentation](http://www.ruby-doc.org/core-2.1.1/)
+- [Official Documentation](http://ruby-doc.org/core)
 - [Ruby from other languages](https://www.ruby-lang.org/en/documentation/ruby-from-other-languages/)
 - [Programming Ruby](http://www.amazon.com/Programming-Ruby-1-9-2-0-Programmers/dp/1937785491/) - An older [free edition](http://ruby-doc.com/docs/ProgrammingRuby/) is available online.
 - [Ruby Style Guide](https://github.com/bbatsov/ruby-style-guide) - A community-driven Ruby coding style guide.