support parameterized arn generation; support elasticmq arn

[hzshlomi]

Here's a quick fix allowing java users of the AWS SDK to get up and running quickly with elasticmq SQS queues registered on the SNS topics.
What I did is basically to transform ARNs starting with "arn:aws:sqs:elasticmq".
Everything i did is configurable, see (env var, configuration file property name):
ELASTICMQ_PREFIX, elasticmq.prefix
ELASTICMQ_ENDPOINT, elasticmq.endpoint
ELASTICMQ_ACCESS, elasticmq.access
ELASTICMQ_SECRET, elasticmq.secret

and also:
SNS_REGION, sns.region
SNS_ACCOUNT, sns.account

to allow control of the generated topic ARNs.
Pls let me know what needs to be done to merge this,
thanks for your work :)
Shlomi

[codecov-io]

Codecov Report

Merging #54 into master will decrease coverage by 1.92%.
The diff coverage is 0%.

@@            Coverage Diff            @@
##           master     #54      +/-   ##
=========================================
- Coverage   40.52%   38.6%   -1.93%     
=========================================
  Files          22      22              
  Lines         422     443      +21     
  Branches       13      18       +5     
=========================================
  Hits          171     171              
- Misses        251     272      +21

Impacted Files	Coverage Δ
.../main/scala/me/snov/sns/actor/SubscribeActor.scala	0% <0%> (ø)	⬆️
src/main/scala/me/snov/sns/Main.scala	0% <0%> (ø)	⬆️

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