Fixed bugs #73, #86, #90

[protspace]

Fixed bugs with wrong layout when content is near the end of the page #73 (comment)
Also could be related to #86, #90

    //bug #1
    document.addSpace(space: 600)
    let section = PDFSection(columnWidths: [0.33, 0.34, 0.33])
    section.columns[0].addText(text: "Lorem ipsum dolor sit amet, consetetur sadipscing elitr, sed diam nonumy eirmod tempor invidunt ut labore et dolore magna aliquyam erat, sed diam voluptua.")
    document.addSection(section)

    document.addText(text: "this text positioned in a wrong way")

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    //bug #2
    document.addSpace(space: 670)
    document.addSpace(space: 70)
    document.addText(text: "this text positioned in a wrong way")

http://prntscr.com/lqac12