opentxs-api: use nullptr instead of NULL

Command used:
    sed -r -i 's/([^[:alpha:]])NULL([^[:alpha:]]|$)/\1nullptr\2/g' "$file"
opentxs-core: use nullptr instead of NULL

Command used:
    sed -r -i 's/([^[:alpha:]])NULL([^[:alpha:]]|$)/\1nullptr\2/g' "$file"
opentxs-ext: use nullptr instead of NULL

Command used:
    sed -r -i 's/([^[:alpha:]])NULL([^[:alpha:]]|$)/\1nullptr\2/g' "$file"
opentxs: use nullptr instead of NULL

Command used:
    sed -r -i 's/([^[:alpha:]])NULL([^[:alpha:]]|$)/\1nullptr\2/g' "$file"
opentxs-script: use nullptr instead of NULL

Command used:
    sed -r -i 's/([^[:alpha:]])NULL([^[:alpha:]]|$)/\1nullptr\2/g' "$file"
opentxs-api include: use nullptr instead of NULL

Command used:
    sed -r -i 's/([^[:alpha:]])NULL([^[:alpha:]]|$)/\1nullptr\2/g' "$file"
opentxs-core include: use nullptr instead of NULL

Command used:
    sed -r -i 's/([^[:alpha:]])NULL([^[:alpha:]]|$)/\1nullptr\2/g' "$file"
Merge pull request #133 from toxeus/useNullptr

Good job :1:
Windows bugfixes after rebase:
- anyoption,hpp was missing #include <cinttypes>
- opentxs.cpp was missing #include <cctype>
- Moved categoryName array from opentxs.hpp to opentxs.cpp.
  It would not compile and the array initialization should
  be in the source file anyway.
Merge pull request #134 from BugFreeSoftware/Rebase_fixes

Windows bugfixes after rebase:
define EXPORT makro in build system