* [core]: define lt_dlinit

... as it appears to be needed by ltdl

define oyGetCurrentDir_() for abstracting getenv(PWD)
* [core]: implement oyGetCurrentDir_()

abstract getenv("PWD") and use GetCurrentDirectory()

use SHGetFolderPath() in windwos part of oyGetHomeDir_()

check arg for oyResolveDirFileName_() to avoid crashes

simplify string construction and allocation in oyResolveDirFileName_()

use new oyGetCurrentDir_()