Update text tool manual page

• Update tool options screenshot and description with default letter spacing option (introduced in 4.4.2)

• Update editor screenshot:

  • color picker and letter spacing were added earlier
  • kerning toggle was added in 4.4.2

• fill and letter-spacing are properly converted between Rich Document <-> SVG now

• Consistently use definition list in text editor section

• letter-spacing and kerning can be controlled from Rich Text editor, not word-spacing though

• Any numeric kerning value other than 0 will be added to current letter-spacing (introduced in 4.4.2)

• Wrap SVG attributes and properties in double-backquotes

• Clarify that "SVG Source" and "Both" are editor modes