Changes in version 0.13:

Ocrad is now able to read pgm files.

The algorithm for space detection is now more scale-independent (uses
rational numbers instead of integers).

The algorithm for space detection in tables have been improved.

Number recognition has been improved.

Variable-size arrays in file block.cc have been replaced by vectors.

Some fixes and small improvements have been made.

Overflow detection is performed when loading or scaling a image file.

A miscompilation when compiling with GCC 3.3.1 has been fixed.
