Do not try to free SSL connection on error

This fixes core dumps that occur occasionally when using an unstable
connection. See issue #47 for details.

Signed-off-by: Lukas Fleischer <info@cryptocrack.de>
Makefile: Do not strip library by default

This allows for using the standard mechanisms for creating debug
packages provided by a lot of package managers. Almost all package
managers invoke strip(1) after the make process anyway, so removing it
won't hurt. You can still invoke `make strip` to strip the dynamic
library when compiling manually.

Signed-off-by: Lukas Fleischer <info@cryptocrack.de>
README.md: Minor wording and formatting changes

Signed-off-by: Lukas Fleischer <info@cryptocrack.de>
Makefile: Add debug target

This allows for easily creating a library with debug symbols by running
`make debug`.

Signed-off-by: Lukas Fleischer <info@cryptocrack.de>
README.md: Add note on including debug symbols

Signed-off-by: Lukas Fleischer <info@cryptocrack.de>
Free cipher contexts

This is targeted at removing the major source of memory leaks described
in issue #13.

Signed-off-by: Lukas Fleischer <info@cryptocrack.de>