Reorganized the documents structure

[haoel]

1. Move the reference document into ./doc/reference directory.
2. Write the ./doc/README.md to index all of the documents.
3. remove the original filters.md and cookbook/README.md.
4. rename the original reference.md to filters.md
5. move all of the images into doc/imgs/ directory.
6. rename the file name, change the _ to -

[suchen-sci]

the new structure of doc looks pretty good!

Is that a good idea to put all images into a single directory?

I find some file name connect words use "_" and some use "-" for example "api_aggregator.md" and "developer-guide.md". Is that a good idea to make all md file use same pattern?

[haoel]

the new structure of doc looks pretty good!

Is that a good idea to put all images into a single directory?

I find some file name connect words use "_" and some use "-" for example "api_aggregator.md" and "developer-guide.md". Is that a good idea to make all md file use same pattern?

those are good ideas, let me work them out!