fix: Style tag must be a block element

[Omikhleia]

Closes #64

Test script

local lunamark = require("lunamark")
local opts = { notes = true }
local writer = lunamark.writer.html.new(opts)
local parse = lunamark.reader.markdown.new(writer, opts)
local result, matadata = parse([[

<style>
.blue20 {
    color: blue;
    font-size: 20px;
}
.red::before {
    color: red;
    content: '_TODO_';
}
</style>

]])

print(result)

Before

<p><style> .blue20 { color: blue; font-size: 20px; } .red::before { color: red; content: &#39;<em>TODO</em>&#39;; } </style></p>

(Lines are not honored, and content is interpreted as Markdown, with escapes ' and <em> tags...)

After

<style>
.blue20 {
    color: blue;
    font-size: 20px;
}
.red::before {
    color: red;
    content: '_TODO_';
}
</style>

(As in original input, unaltered)