Added the ability to add a content to the header

[brutu33]

Added the ability to add to the header all the same as in the body of the document except for pagebreak
Calling from code same as simple other commands, but through header object :

docx.header.img ......
docx.header.hr ....
docx.header.h1 .....

Example:

Caracal::Document.render(filename) do |docx|
  docx.header.h1 'Page 1 Header'
  docx.header.img "http://example.com/image.png" do
    width  60
    height 60
    align :right
  end

  docx.header.p "skdanflksamlkdfmlaksd"

  docx.header.table [['11', '1213', '14'], ['21', '22', '23', '24']] do
    cell_style rows[0][0], rowspan: 2
    cell_style rows[0][1], colspan: 2
    cell_style rows[0][2], rowspan: 2
  end

  docx.header.p do
    text 'Here is a sentence with a '
    link 'link', 'https://www.google.com'
    text ' to something awesome', font: 'Courier New', color: '555555', size: 32, bold: true, italic: true, underline: true, bgcolor: 'cccccc'
    text '.'
    br
    text 'This text follows a line break and uses a character style instead of overrides.', style: 'MyCharStyle'
    page
  end

  docx.header.ol do
    li 'First item'
    li do
      text 'Second item with a '
      link 'link', "http://example.com/image.png"
      text '.'
      br
      text 'This sentence follows a line break.'
    end
  end

  docx.header.hr
end

[jdugan]

Hei! Thanks for this.

I'm on holiday right now, so I haven't had a chance to look at your commit closely (or even quickly, if I'm being honest), but your description is in line with the thoughts I outlined in the pending issue, so I'll be interested to review the changes when I'm back at my desk.

I'll be in touch.

[allomov]

Hey, @jdugan. Could you please take a look on this PR and give you feedback? Thank you.

[Passerby]

+1

[benjaminketron]

Hi @jdugan, :)

Is there anything i can do to help this PR along?