fixed typo, purely cosmetic

"executable" was written as "exectuble" and "exectuable"
Merge pull request #721 from SpiritQuaddicted/patch-1

fixed typo, purely cosmetic
[build] Add CMake Build System

  - Reflect the httpserver->fileserver changes
  - Set SOVERSION of libseafile to 0 as the same as what autoconf scripts do
[build] cmake fix

  - fix header install issue
  - remove key storage stuff