A few updates to the pdf device

Ensure that only base14 fonts are used
Set BaseFont using the name from the font
Use WinAnsiEncoding
Derive the font size from the trm matrix
Add support for freetext annotations

This initial commit doesn't entirely complete the task:
1) There are a couple of ucs<->winansi conversions left out,
2) The text displayed by the appearance string can slightly
overflow the annotation rectangle.
Change pdf_measure_text to account for the borders around characters

Prevously the true bounds of the glyph were used which didn't account
for the total area blocked out by a character
For freetext annotations, distinguish device and page space correctly.
Fix signature-support build
Improve naming consistency
Handle more color cases in DA handling
Correctly account for alterations to xobject matrix and bbox
Use ascender and descender to determine line skip

We should use the leading, if present, and if not present we should
probably use a value a little greater than the sum of the ascender
and descender, but this is definitely a step in the right direction
and improves the look of filled-in forms.
Add support for creating signature-field appearance streams
Insert the extra layers required for a signature-appearance stream
Remove unnecessary parameter
Signature creation
pdfapp.c: Enable horizontal mouse scrolling.

This patch handles mouse buttons 6 and 7 and scrolls the page accordingly.
Implement continuous scrolling with 'j' and 'k'.