Fix hotspot churn report crash where a folder is found (can happen with submodules)

Churn hotspot no longer tries to read directories as if they were files
Remove annoying debug in Hotspot and correct typo
Update History
Add Entity-Relationship Diagrams
Generate CONTRIBUTORS list, ranking by most code changes to least
Sign gem and add bf4.pem
Bump to 4.5.0
Add checksum of 4.5.0 built gem
Adding missing signing_key to gemspec

per http://developer.zendesk.com/blog/2013/02/03/signing-gems/
    and https://github.com/sferik/twitter/blob/master/twitter.gemspec

1. Create self-signed cert

 cd ~/.ssh
 gem cert --build your@email.com
 chmod 600 gem-p*

2. Configure gem cert (I'm calling mine bf4)

 mkdir certs
 cp ~/.ssh/gem-public_cert.pem certs/bf4.pem
 - commit the pem
 - Add to gemspec
 s.cert_chain  = ['certs/bf4.pem']
 s.signing_key = File.expand_path("~/.ssh/gem-private_key.pem") if $0 =~ /gem\z/

3. Add your own cert, just like anyone else

 gem cert --add certs/bf4.pem

4. Build gem and test that you can install it

 gem build metric_fu.gemspec
 gem install metric_fu-4.5.1.gem -P HighSecurity
Bump to 4.5.1; yank 4.5.0 due to bad build
Add checksum for built 4.5.1 gem
Revise gemspec to exclude etc dir. erd.png is 1.1MB
Bump to version 4.5.2
Pirate bundler gem helpers; add checksum task
Add checksum for metric_fu-4.5.2.gem
add template configuration methods
refactoring templates configuration
Remove annoying debug in Hotspot and correct typo
Update History
Add Entity-Relationship Diagrams