Support optional pump event synchronization

NEW: The following synchronization feature is disabled by default, but can be enabled via the --features flag:

PUMP_EVENTS: Events reported by the pump. Includes support for the following:

• Site/Cartridge Change (occurs for both a site change and a cartridge change)
• Empty Cartridge/Pump Shutdown (from my investigation, occurs either when the cartridge runs out of insulin OR you hard-shut off the pump)
• User Suspended (occurs when you manually disable insulin delivery)
• Exercise Mode (in Nightscout, appears with a start and end time)
• Sleep Mode (in Nightscout, appears with a start and end time)

v0.5

• Tracks manual pump suspensions (e.g., human-initiated "stop insulin" events) as a 0u/hr basal in Nightscout (#17)