Improved <a> tag handling & optional <li> list formatting

Changes:

• another fully-backward-compatible update
• tag is now case-insensitive and follows official specs, see #16
• added optional WithListSupport and WithListSupportPrefix to make <li></li> lines formatted with a prefix like " - "

v1.1.0

• same as v1.0.9, just signaling the fact that the new functionality has been added
• fully-backward-compatible update (with any past version)
• functional options (line breaks style and tag inner text preservation)

  HTML2TextWithOptions(`click <a href="http://bit.ly/2n4wXRs">news</a>`, WithLinksInnerText())
  // produces: click news <http://bit.ly/2n4wXRs>

v1.0.9

• fully-backward-compatible update
• functional options (line breaks style and tag inner text preservation)

  HTML2TextWithOptions(`click <a href="http://bit.ly/2n4wXRs">news</a>`, WithLinksInnerText())
  // produces: click news <http://bit.ly/2n4wXRs>

v1.0.7

Fix tag pattern to support custom tags starting with 'a' character like <attribute>test</attribute> and return inner content test.

v1.0.6

fix: allow # in link URLs and prevent unnecessary space, fixes #11

1.0.5

Fix to prevent lower-casing "href" attribute of tags

1.0.4

Configurable line break style (backward-compatible CrLf is default) and numerical html entities, both contributed by @merlincox.