Exception changes

[cjdrake]

Recently became familiar with the Google Python Style Guide.

The way they name exceptions is nice and simple. If some module needs to define an exception type, it's just named Error. Then you use it like except module.Error.

This affects the following exceptions:

• [x] LexError => pyeda.parsing.lex.Error
• [x] LexCompileError => pyeda.parsing.lex.CompileError
• [x] LexRunError => pyeda.parsing.lex.RunError
• [x] BoolExprParseError => pyeda.parsing.boolexpr.Error
• [x] DIMACSError => pyeda.parsing.dimacs.Error
• [x] PLAError => pyeda.parsing.pla.Error
• [x] EspressoError => pyeda.boolalg.espresso.Error
• [x] PicosatError => pyeda.boolalg.picosat.Error