Add gittalk supoort and fixed a bug

[anribras]

1 Add gittalk support;
2 Fixed render error bug after changing any contents in _post

To use it , add some configuration in _config.yaml and enable = true

gittalk:
  enable: false
  clientID: # youridxyz
  clientSecret: # yourid123 
  repo: # yourid.github.io
  owner: # yourid 
  admin: # yourid same as owner