Parse files listed via STDIN

wdd_select can now parse more than one file and the list of files can be
passed via STDIN to allow for nicer piping.

Example:

```bash
$ find data_samples -name "*.html" | wdd_select "head, body"
data_samples/forecast_io.html,head
data_samples/forecast_io.html,body
data_samples/jimsmarketingblog_com.html,head
data_samples/jimsmarketingblog_com.html,body
```
addd STDIN input for wdd_tag_count
Merge pull request #4 from Webdevdata/feature/parse_files_listed_via_STDIN

Parse files listed via STDIN