Merge pull request #17 from shockjiang/master

Zipf-Mandelbrot app support
zipf: Small changes (style and small logic correction) and adding documentation section
docs: zipf figure update
apps: Adding additional NS-3 attribute to control the overall number of sent Interest (previously, application runtime defined total number of Interests)
Enabling trace sources for Interest-Data lifetimes
tracers: simplification of ndn::CsTracer (there no real need for virtual calls)
app+utils+doc: Adding application-level trace helper to record Interest-Data delays
src bug: Adding missing topology files

Wrong wildcard in gitignore prevented them to be commited earlier
utils: Bug with new app-delay-tracer.  FullDelay was connected to the wrong tracesource
docs: add description of generated file by ndn::AppDelayTracer
apps+utils: Correcting Interest-Delay tracing
apps+model+utils: Implementing Interest/Data hop counting using new PacketTag
docs: Extending and reorganizing documentation. Adding basic description about forwarding strategies enforcing Interest limits
plugins+tools: Adding experimental RocketfuelMapReader and tool to convert topology from .cch format into annotated topology format
plugins-topology: Fixing compilation problem - back-converting c++11 syntax

closes #20
model: An experimental support for LFU replacement policy (need further adjustments)
helper+utils:  Small extension of global routing helper and restoring several IP-based metric collectors, including Ipv4RateL3Tracer
Fixing bugs related to NACKs implementation
utils: Porting several new IPv4 tracers from the old code. Extending ndn-app-delay-tracer
apps: Add more configurability to ndn::ConsumerWindow

By default, it will zero out the window upon timeout