save tracing data to file.

[Aries]

Hi all:     I have noticed that skywalking use heap buffer to cache tracing 
data. It usually cause data loss. Because of this problem, I want to add a 
high-performance  file storage to skywalking,so that tracing data can be saved 
to disk.      If tracing data saved to file,skywalking will have strong ability 
to accumulate data and we do not have to care about how many tracing data 
provided or whether  OAP server working, data had saved.     Do we need this 
feature? Any suggestions?            Thanks