consider exporting objects being used by `SpaDES.core`

[achubaty]

SpaDES.core currently has:

extractFromCache <- getFromNamespace("extractFromCache", "reproducible")
fileExt <- getFromNamespace("fileExt", "reproducible")
filePathSansExt <- getFromNamespace("filePathSansExt", "reproducible")
getDrv <- getFromNamespace("getDrv", "reproducible")
isWindows <- getFromNamespace("isWindows", "reproducible")
isAbsolutePath <- getFromNamespace("isAbsolutePath", "reproducible")
isRaster <- getFromNamespace("isRaster", "reproducible")
isSpat <- getFromNamespace("isSpat", "reproducible")
layerNamesDelimiter <- getFromNamespace("layerNamesDelimiter", "reproducible")
loadFile <- getFromNamespace("loadFile", "reproducible")
makeAbsolute <- getFromNamespace("makeAbsolute", "reproducible")
remapFilenames <- getFromNamespace("remapFilenames", "reproducible")

these should be properly exported by reproducible for use with other packages, even if they are inteded for 'developers' and not for users.