(SERVER-4) Add memory check to Master Service

Add a memory check to the Master service's init function that,
when the /proc/meminfo file exists, parses it to get the total
amount of RAM on the system and fails if the total JVM heap
size is greater than 90% of RAM.
(SERVER-4) Address PR comments

Extract memory check into separate function in core namespace.
Throw error instead of exception when there is not enough memory.
Improve "Not Enough Memory" error message to more accurately
reflect required RAM. Use me.raynes.fs instead of clojure.java.io
(SERVER-4) Change memory-check function name

Change the name of the memory-check function to
validate-memory-requirements!. Remove use of FileInputStream
from this function.
(SERVER-4) Remove unused import

Remove unused FileInputStream import.
(SERVER-4) Improve required RAM calculation

Improve the required RAM calculation to make it clearer.
Merge pull request #201 from fpringvaldsen/server-4-fail-when-too-little-ram

(SERVER-4) Add memory check to Master Service