Merge pull request softhsm#501 from randombit/remove-eol-botan-support

Remove support for obsolete/EOL versions of Botan.

We really need to move away from the really outdated version of Botan, this pull requests looks good and drops a not of ifdefs that are no longer needed.  This change needs to be made prominent in the NEWS file and in the announcement (will make this change and to appveyor a bit later).

.travis.yml

@@ -1,10 +1,12 @@
 language: cpp
+dist: bionic
 compiler:
   - gcc
   - clang
 before_install:
+  - sudo add-apt-repository -y ppa:ubuntu-backports-testers/ppa
   - sudo apt-get update -qq
-  - sudo apt-get install build-essential autoconf automake libtool libcppunit-dev libsqlite3-dev sqlite3 libbotan1.10-dev libssl-dev p11-kit
+  - sudo apt-get install build-essential autoconf automake libtool libcppunit-dev libsqlite3-dev sqlite3 libbotan-2-dev libssl-dev p11-kit
 script: sh testing/travis/travis.sh
 env:
   - CRYPTO=openssl OBJSTORE=file

README.md

@@ -35,11 +35,11 @@ because of the PKCS#11 interface.
 SoftHSM depends on a cryptographic library, Botan or OpenSSL.
 Minimum required versions:
 
-- Botan 1.10.0 
+- Botan 2.0.0
 - OpenSSL 1.0.0
 
-If you are using Botan, make sure that it has support for GNU MP (--with-gnump).
-This will improve the performance when doing public key operations.
+If you are using Botan, use at least version 2.6.0. This will improve
+the performance when doing public key operations.
 
 The GNU Autotools (Autoconf, Automake, Libtool) are also required for building
 the software. It is also recommended to install pkg-config so that the