Rewrite Configure to handle the target values as hash tables.

The reasoning is that configuration strings are hard to read and error
prone, and that a better way would be for them to be key => value hashes.

Configure is made to be able to handle target configuration values as a
string as well as a hash.  It also does the best it can to combine a
"debug-foo" target with a "foo" target, given that they are similar
except for the cflags and lflags values.  The latter are spliced into
options that are common for "debug-foo" and "foo", options that exist
only with "debug-foo" and options that exist only with "foo", and make
them into combinable attributes that holds common cflags, extra cflags
for debuggin and extra cflags for non-debugging configurations.

The next step is to make it possible to have template configurations.

Reviewed-by: Andy Polyakov <appro@openssl.org>