Metadata cleanup

This commit:

* Adds a Gemfile so that Bundler can be used to install dependencies.
* Puts Gemfile.lock in .gitignore, since that file shouldn't be in source
  control.
* Specifies Shoulda as a development dependency in the gemspec file.
* Converts tabs to spaces in the gemspec file.

.gitignore

@@ -2,3 +2,4 @@
 doc/
 coverage/
 *.gem
+Gemfile.lock

Gemfile

@@ -0,0 +1,3 @@
+source "http://rubygems.org"
+
+gemspec

finance.gemspec

@@ -2,19 +2,20 @@ require 'rubygems'
 require 'rake'
 
 SPEC = Gem::Specification.new do |s|
-	s.name = "finance"
-	s.version = "1.1.2"
-	s.author = "Bill Kranec"
-	s.email = "[email protected]"
-	s.platform = Gem::Platform::RUBY
-	s.summary = "a library for financial modelling in Ruby."
-	s.description = "The finance library provides a Ruby interface for working with interest rates, mortgage amortization, and cashflows (NPV, IRR, etc.)."
-	s.homepage = "https://rubygems.org/gems/finance"
+  s.name = "finance"
+  s.version = "1.1.2"
+  s.author = "Bill Kranec"
+  s.email = "[email protected]"
+  s.platform = Gem::Platform::RUBY
+  s.summary = "a library for financial modelling in Ruby."
+  s.description = "The finance library provides a Ruby interface for working with interest rates, mortgage amortization, and cashflows (NPV, IRR, etc.)."
+  s.homepage = "https://rubygems.org/gems/finance"
 
   s.required_ruby_version = '>=1.9'
-	s.add_dependency 'flt', '>=1.3.0'
-	s.files = FileList['README', 'COPYING', 'COPYING.LESSER', 'HISTORY', 'lib/**/*.rb', 'test/**/*.rb'].to_a
+  s.add_dependency 'flt', '>=1.3.0'
+  s.add_development_dependency 'shoulda', '3.1.1'
+  s.files = FileList['README', 'COPYING', 'COPYING.LESSER', 'HISTORY', 'lib/**/*.rb', 'test/**/*.rb'].to_a
 
-	s.has_rdoc = true
-	s.extra_rdoc_files = ['README', 'COPYING', 'COPYING.LESSER', 'HISTORY']
+  s.has_rdoc = true
+  s.extra_rdoc_files = ['README', 'COPYING', 'COPYING.LESSER', 'HISTORY']
 end