.NET 3.5 Compatibility

As described here:
https://github.com/jaymedavis/stripe.net/issues/26#issuecomment-6225018
Full support for 3.5 compatible nuget build

Should allow complete 3.5 support for Stripe.net's Nuget.
Removing binaries / modifying gitignore

Accidentally missed these binaries not being ignored initially...
removed.
Defining NET40

Forgot to define NET40 in the primary csproj. Fixed.
Merge pull request #1 from jaymedavis/master

Latest from jaymedavis/stripe.net
Merge pull request #2 from iATN/master

Latest from jaymedavis/stripe.net
Integrating StripeBankAccount.cs into .NET 3.5 project
Add JsonIgnore attribute to properties that are *hijacked* through *Internal properties.
fixes #233
little cleanup from the camel case contract resolver
cleaned up merging for 3.5 support and bumped version