Fix Linux build problems

[ngaro]

• Adds 2 missing headers needed for compiling
• Removes a definition already defined earlier (not necessary)
• Fixes problems with incorrect gcc options
• Automatically download and build the correct version of openssl
• Add possibility for cleaning the build environment

[Ri1a]

I changed the lines you committed, but I still got one error:

"gcc: error: ../heartleech/heartleech.c: No such file or directory"

I also reinstalled it and modified the path, but this didn't help. Did I do sth wrong?

[ngaro]

I tried it again here, works fine. You must be compiling it wrong.
I can compile my rep like this:
git clone git@github.com:ngaro/heartleech.git && cd heartleech && make

[Ri1a]

To entirely fix the Linux build problems you should also add the -I flag to openssl/libssl.a and openssl/libcrypto.a

[Ri1a]

added -I flags to openssl/libssl.a and openssl/libcrypto.a

[Ri1a]

Suggested change

	gcc heartleech.c -I openssl -I openssl/include -I openssl/crypto/include -I openssl/ssl -I openssl/libssl.a -I openssl/libcrypto.a -ldl -lpthread -o heartleech