tracing support

[kanpov]

Under a feature-gate.
On the wishlist for 0.2/0.3.

[kanpov]

Postponed for 0.3, also evaluating fastrace as an alternative.

[kanpov]

Postponed for 0.5/0.6 :)

[kanpov]

Postponed for 0.3, also evaluating fastrace as an alternative.

Slight update: fastrace is not yet widely adopted and is also pretty immature, so not going to use it. Using log instead of tracing also isn't great, as fctools is a decisively async toolkit, which is what tracing gears to.

[kanpov]

Low priority, postponed for later. In my production applications using fctools, there is little necessity to add more tracing from inside fctools. If anybody has real demand for this, let me know by writing on this issue.