Added Goleveldb store

[ppizarro]

• Added Goleveldb store and make it default
• Add Close to KVReader interface

[codecov-io]

Current coverage is 58.25%

Merging #43 into master will increase coverage by +0.61% as of 5885adb

@@            master     #43   diff @@
======================================
  Files           21      22     +1
  Stmts         1636    1689    +53
  Branches         0       0       
  Methods          0       0       
======================================
+ Hit            943     984    +41
  Partial          0       0       
- Missed         693     705    +12

Review entire Coverage Diff as of 5885adb

---

Uncovered Suggestions

1. +1.07% via ...b/neosearch/index.go#210...227
2. +1.01% via ...osearch/cache/lru.go#132...148
3. +1.01% via ...arch/index/filter.go#10...26
4. See 7 more...

Powered by Codecov. Updated on successful CI builds.

[i4ki]

Nice!

Now the project is go-gettable with no external dependencies! I will remove the environment variables CGO_LDFLAGS, CGOCFLAGS and LD* flags from our travis config in the UI interface.

I've two questions:

Now, the -tags option for builds does't works anymore? Or I still can use -tags to switch between default storage engine?

And, after this merge, we can mix storage engines for an index?

=)

[ppizarro]

We can use -tags leveldb to compile support to leveldb storage but we can't change the default storage goleveldb to leveldb. It's hardcode the default storage to goleveldb.

I'll create a issue to config the default storage.