Added 'Get started quickly' section
Remove a compiler warning

In 7b48ac95, the bufcstr prototype has been changed. This lead to a
warning since bufgrow is meant to change the allocated size to the given
buffer but the latter is a const.
Merge pull request #355 from vmg/buffer-warning

Remove a compiler warning
Merge pull request #353 from evolve2k/patch-1

Added 'Get started quickly' section to README [ci skip]
Follow up to #353 [ci skip]

Improve a bit the README and use 1.9 hash syntax in code examples
Change MKDEXT_NO_INTRA_EMPHASIS to not start after alphanumerics

No behavior should change if the NO_INTRA_EMPHASIS flag is not set.
With it
set, the following behavior changes should be seen:  (The parentheses
in the
following examples can be replaced by any non-alphanumeric character.)

- "(_italics_)" is italic
- "this(_is_)weird" italicizes the "is"

We were already checking for non-alphanumerics  on the closing boundary;
that is, "_this_()" would have rendered as italicized even though the
closing
underscore wasn't followed by a space. This commit just brings the same
behavior to the opening underscore.
Update README.markdown
Merge pull request #362 from nemesis/patch-1

Update README.markdown [ci skip]
Merge pull request #361 from bigjason/intra-emph-refine

Change MKDEXT_NO_INTRA_EMPHASIS to not start after alphanumerics
Add a changelog entry for #361 [ci skip]
Avoid adding extra conditions

If `isalnum` returns true for the given char, the latter will be
different from `>` or ')' anyway. The introducing commit is e153686c.
Fix typo
Merge pull request #364 from mrueg/master

Fix typo
Merge pull request #363 from vmg/follow-up-361

Follow up to #361
Introduce _isalnum checking ASCII alphanumerics

`_isalnum` checks if the given character is an alphanumeric character
in the ASCII range. (The code is borrowed from github-markdow.)

This commit enables emphasis inside of sentences in multi-byte languages
when the the NO_INTRA_EMPHASIS flag is set.

For example, given the following sentence (in Chinese):

    中文內無空白的**粗體**也應加粗。

The two characters surrounded by asterisks should be bold.

This frees multi-byte language users from adding extra spaces into
sentences and is exactly how markdown on Github behaves.
Merge pull request #366 from Domon/intra-emph-multibyte

Enable emphasis in multi-byte sentences when no_intra_emphasis is set
Remove the testing part from the README [ci skip]

This is already explained in the contribution guideline
Remove the yielding of anchors in the header callback

This basically reverts facd5c5a. We should not change any method's
arity between point releases.
Fix fragment (#) links
update array length