Add MIME type for text (issue: #88)

[sshota0809]

this is related to issue #88

I tried to add MIME type for text.

Following main.go is to Match sample.html

$ od -N14 -hc sample.html 
0000000      213c    6f64    7463    7079    2065    7468    6c6d        
           <   !   d   o   c   t   y   p   e       h   t   m   l        
0000016

$ go run main.go 
File type: html. MIME: application/html

Please review my code and consider to merge my this.

Best regards.

[h2non]

This library is not intended to work with text-based files with arbitrary content within that might or might not be compliment with a specific content format. It's only intended to work with binary files that expose a deterministic magic number bytes header within them.

For text-based inference format, a different matching strategy should be used, as done here:
https://github.com/h2non/go-is-svg