hline&vline (log scale support)

A modification of Brandon Kuczenski's hline and vline to add support for log scales

Improvements on original :

• Support for semilog & loglog plots
• Text handle access for post processing: changing text string, color, etc.
• Additional optional input for x-position (hline) or y-position (vline) of text
• Compactifying input processing

Many more improvements are possible. These are just the ones I have commonly needed. Suggestions for improvements are welcome.