Makefile: only build libplepaper.a, not libplepaper.so

Now that all the PLSDK libraries are packaged into a single
libplsdk.so, there is no need to keep individual shared
libraries.
add PLEP_CLEAR_ON_EXIT hardware option

* add PLEP_CLEAR_ON_EXIT hardware option to enum plep_hw_opt to
  ask the ePDC to clear the screen when it is removed when the
  value is 1, or not clear the screen with a value of 0
* add _PLEP_HW_OPT_N_ to enum plep_hw_opt to know how many
  hardware options are available and use it in assert statements
  in plep_{get|set}_hw_opt functions
add setver.sh script to set the library version string

This script takes care of updating the library version
string in libpldraw.h and adds it to the git index for
automatic version update when running release script.
ChangeLog v1.7 -> v1.8