Merged #103. Last pre-release prior to GA release for support of v2 Intake API.

Thanks your @FreezeWarp

Use the automagic destruct function in Agent::__destruct to send the payload on object destroy

This is the first release candidate of v7.x with support of:

• the v2 Intake API of Elastic APM
• Distributed Tracing

• added support for Span event
• correct content encoding, gzip

Agent Beta RC.1 Release

• support of v2 Intake API
• setting of parent transactions in transaction and errors
• metricset event
• more examples

• Reset stores after send on not active agent #75
• Add custom request context #74

• support for proxy'ied IP
• fixes in documentation

Forwarding of proxy/load balanced IP's (#64 )

Bugfixes and enhancements

Allow explicit Timer init; PR #49 thank you @dstepe