Add image processing examples (#658) [skip ci]

* add inplace image processing example

* add s3 upload example

* update dockerfile

* for some reason, I need to include json if using ruby:dev

* update read me

* strip stdin input

Author: c0ze

examples/image_processing/inplace/.gitignore

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+bundle/
+.bundle/
+func.yaml
+Gemfile.lock
+*.png

examples/image_processing/inplace/Dockerfile

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+FROM iron/ruby:dev
+RUN apk --no-cache --update add imagemagick
+
+COPY ./ /func
+WORKDIR /func
+
+RUN gem install bundler --no-ri --no-rdoc
+RUN bundle
+
+ENTRYPOINT bundle exec ruby func.rb

examples/image_processing/inplace/Gemfile

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+source 'https://rubygems.org'
+
+gem 'json'
+gem 'mini_magick'

examples/image_processing/inplace/README.md

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+## Image processing with Ruby Example
+
+This example will show you how to process images with a Ruby function.
+
+```sh
+# create your func.yaml file
+fn init <YOUR_DOCKERHUB_USERNAME>/image-processing
+
+# build the function
+fn build
+
+# test it
+echo "http://www.sourcecertain.com/img/Example.png" | fn run > image.png
+
+# push it to Docker Hub
+fn push
+
+# Create a route to this function on IronFunctions (assuming you have an app called `test`)
+fn routes create test /image-processing
+
+# you can now access via curl as well
+curl -v -X POST http://localhost:8080/r/test/image-processing -d "http://www.sourcecertain.com/img/Example.png" > image.png
+```
+

examples/image_processing/inplace/func.rb

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+require 'mini_magick'
+
+payload = STDIN.read.strip
+image = MiniMagick::Image.open(payload)
+image.contrast
+image.resize "250x200"
+image.rotate "-90"
+image.write STDOUT

examples/image_processing/s3upload/.gitignore

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+bundle/
+.bundle/
+func.yaml
+Gemfile.lock
+*.png

examples/image_processing/s3upload/Dockerfile

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+FROM iron/ruby:dev
+RUN apk --no-cache --update add imagemagick
+
+COPY ./ /func
+WORKDIR /func
+
+RUN gem install bundler --no-ri --no-rdoc
+RUN bundle
+
+ENV AWS_ACCESS_KEY_ID {add your id here}
+ENV AWS_SECRET_ACCESS_KEY {add your key here}
+ENV AWS_S3_BUCKET iron-functions-image-resize
+ENV AWS_REGION us-east-1
+
+ENTRYPOINT bundle exec ruby func.rb

examples/image_processing/s3upload/Gemfile

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+source 'https://rubygems.org'
+
+gem 'json'
+gem 'mini_magick'
+gem 'aws-sdk-s3', '~> 1'

examples/image_processing/s3upload/README.md

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+## Image processing with Ruby Example, Upload to S3
+
+This example will show you how to process images with a Ruby function, and upload to a S3 bucket.
+
+```sh
+# create your func.yaml file
+fn init <YOUR_DOCKERHUB_USERNAME>/image-processing
+
+# build the function
+fn build
+
+# test it
+echo "http://www.sourcecertain.com/img/Example.png" | fn run
+
+# push it to Docker Hub
+fn push
+
+# Create a route to this function on IronFunctions (assuming you have an app called `test`)
+fn routes create test /image-processing
+
+# you can now access via curl as well
+curl -v -X POST http://localhost:8080/r/test/image-processing -d "https://www.nationalgeographic.com/content/dam/science/photos/000/010/1086.ngsversion.1491440409220.adapt.1900.1.jpg"
+> https://iron-functions-image-resize.s3.amazonaws.com/1086.ngsversion.1491440409220.adapt.1900.1.jpg
+```
+

examples/image_processing/s3upload/func.rb

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+require 'mini_magick'
+require 'aws-sdk-s3'
+
+file_uri = STDIN.read.strip
+image = MiniMagick::Image.open(file_uri)
+image.contrast
+image.resize "250x200"
+image.rotate "-90"
+
+s3 = Aws::S3::Client.new
+bucket = ENV['AWS_S3_BUCKET']
+
+obj = s3.put_object( bucket: bucket,
+                     key: File.basename(file_uri),
+                     body: image.tempfile,
+                     acl: "public-read",
+                     cache_control: "max-age=604800")
+
+# Unfortunately put_object returns `put object output`, not an object.
+# So we create another reference here. Probably there is a better way to do this in S3 API.
+obj = Aws::S3::Object.new bucket_name: bucket, key: File.basename(file_uri)
+puts obj.public_url