[Add] get/set varnames for dataset or table

Signed-off-by: Oleg Komarov <o.komarov11@imperial.ac.uk>
[Change] yyyymmdd2serial: implicit conversion to double

Signed-off-by: Oleg Komarov <o.komarov11@imperial.ac.uk>
[Add] isfeatchage: returns index to earliest in time change of feature

Signed-off-by: Oleg Komarov <o.komarov11@imperial.ac.uk>
[Minor] added nan2zero + other

Signed-off-by: Oleg Komarov <o.komarov11@imperial.ac.uk>
[Add/Change] pivotFromTo and used inside importDsp500list

Signed-off-by: Oleg Komarov <o.komarov11@imperial.ac.uk>
[Add] sampledates: samples from a table (spreading/reducing)

Signed-off-by: Oleg Komarov <o.komarov11@imperial.ac.uk>
[Add] sp500intraday #1

Signed-off-by: Oleg Komarov <o.komarov11@imperial.ac.uk>