Add [button] shortcode

[kpettinga]

[button url="" size="" style=""]text[/button]

Should have the following attributes:

Attribute	Description/Choices/Default
url	web address (required)
size	"small" / default: ""
style	"solid" / default: ""

Markup examples:

default <a href="$url" class="ccl-b-btn">Button text</a>

size="small" <a href="$url" class="ccl-b-btn ccl-is-small">Button text</a>

style="solid" <a href="$url" class="ccl-b-btn ccl-is-solid">Button text</a>

[davekellam]

[button] shortcode is now implemented with url, size and style attributes.