3.4.0

This release is long overdue. It includes coupon support, improved admin,
fixing some bugs and deprecation warnings, support for taxes on subscriptions
and handling unicode in customers names.

• PR 259 (Vadim) - country is blankable now for Card objects
• PR 292 (Russell Keith-Magee) - handle unicode characters in customer names
• PR 299 (Russell Keith-Magee) - add template tag for stripe public key
• PR 302 (Ryan Verner) - tax support to subscriptions
• PR 304 (Russell Keith-Magee) - enable charge immediately option on subscription update
• PR 303 (Russell Keith-Magee) - coupon support
• PR 305 (Russell Keith-Magee) - protect against duplicate customer creation
• PR 307 (Adam Duren) - do not require customer to create a charge
• PR 313 (Ian R-P) - update to handle change in exception message from stripe for customer not found
• PR 316 (Charlie Denton) - doc updates
• PR 317 (Charlie Denton) - fixes failed charge webhook processing
• PR 319 (Charlie Denton) - allow customers to be created with qty > 1 of a subscription plan
• PR 323 (Charlie Denton) - fix packaging to prevent jsonfield 2+ from installing
• PR 324 (Charlie Denton) - gracefully handle invoice creation failure
• PR 295, PR 291, PR 288, PR 286 (Mariusz Felisiak) - fixed deprecation warnings