refactor phase2
remove strconv
fix bug in updateMaxInstanceNum
Merge pull request #33 from xiangli-cmu/refactor_phase2

refactor phase_2
add doc for instance doc
refine doc
Merge pull request #34 from fengjingchao/doc

add doc for instance doc
Merge branch 'dev' of github.com:go-epaxos/epaxos into dev

Conflicts:
	replica/phase2.go