gitDataUrl: Convert ulr-name for reading in raw-mode
Description
This functions converts a given urlName so that from data from git-hub can be read correctly that tabular data.
Thus, this will remove '/blob/' and change starting characters to 'raw.githubusercontent.com'
(NULL or matrix) adjust/ custom-modify search- and replacement items; should be matrix with 2 columns,
the 1st colimn entries will be used as 'search-for' and the 2nd as 'replace by' fro each row.
silent
(logical) suppress messages
debug
(logical) additional messages for debugging
callFrom
(character) allow easier tracking of messages produced