Change unite strategy

-   Rename sources/kinds names to prevent confliction with other plugins
-   Introduce unite-filters (Fixed issue #6)
    -   converter_gista_full
    -   converter_gista_short
    -   converter_gista_without_gistid
    -   converter_gista_without_datetime
    -   converter_gista_without_date
    -   converter_gista_without_time
-   Remove narrowing, introduce unite#start_temporary (Fixed issue #8)
-   Introduce unite-kind-uri (Fixed issue #7)
-   Introduce smart_open features (Fixed issue #5)
-   Introduce 'post_to_gist' action to file, buffer kinds (Fixed issue
    #10)
-   Fix Unite.vim issue (Fixed issue #11)
-   Fix :Gista --disconnect issue (Fixed issue #12)
Improve documentations for new implementations
Bump version