go.tools/cmd/cover: use html/template for html generation
go.tools/cmd/cover: use html/template for html generation

Also includes simple JavaScript dropdown picker.

R=golang-dev, r
CC=golang-dev
https://codereview.appspot.com/10838045

webfd/go-zh.tools,webfd/go-zh.tools,karmakaze/go.tools,chenjianlong/go.tools,8limbs/gotools,karmakaze/go.tools,bryanxu/go-zh.tools,8limbs/gotools,webfd/go-zh.tools,chenjianlong/go.tools,d0f/go-zh.tools,skyportsystems/go.tools,karmakaze/go.tools,bryanxu/go-zh.tools,lattera/go.tools,skyportsystems/go.tools,chenjianlong/go.tools,skyportsystems/go.tools,d0f/go-zh.tools,lattera/go.tools,skyportsystems/go.tools,d0f/go-zh.tools,d0f/go-zh.tools,bryanxu/go-zh.tools,karmakaze/go.tools,webfd/go-zh.tools,bryanxu/go-zh.tools,bryanxu/go-zh.tools,karmakaze/go.tools,d0f/go-zh.tools,lattera/go.tools,skyportsystems/go.tools,8limbs/gotools,webfd/go-zh.tools