Enclose selected text in <blockquote> in description field

Pinboard allows <blockquote> tags for quotes in link
descriptions; I typically use these to indicate what
parts of the description are my notes vs. what is content
from the original page.
Merge pull request #12 from cdzombak/selection-blockquote

Enclose selected text in <blockquote> in description field
Add explanation for blockquote tag in description
mv img to img folder
New in settings: private always checked
icon update
add @tamimat
去掉重复的tag
Merge pull request #13 from seansay/remove-duplicated-tags

去掉重复的tag
check response prevent error
latest version number