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.

[eliotmcintire]

I think this would be fine... but it would probably be easier if we change the function names to use the "dot" starting character so that users don't see them by default. Obviously we would need to do that in SpaDES.core also.