Update version string format to PEP 440.
Update version string format to PEP 440.

Was using [branch-]1.2.3[-beta04] but this does not match PEP 440.  I
now use 1.2.3[b4][+branch].  I also remove dashes from the branch name.

So "fix-bug-1.2.3-beta04" would now be "1.2.3b4+fixbug".

vegitron/pyodbc,adrinjalali/pyodbc,adrinjalali/pyodbc,devintjones/pyodbc,vegitron/pyodbc,devintjones/pyodbc,FlipperPA/pyodbc,vegitron/pyodbc,pyparallel/pxodbc,pyparallel/pxodbc,FlipperPA/pyodbc,romainr/pyodbc,adrinjalali/pyodbc,romainr/pyodbc,romainr/pyodbc,FlipperPA/pyodbc,uber/pyodbc,uber/pyodbc,pyparallel/pxodbc,uber/pyodbc,devintjones/pyodbc