Add (let) & better literal handling to API.
Add (let) & better literal handling to API.

ucscXena/ucsc-xena-server,acthp/ucsc-xena-server,ucscXena/ucsc-xena-server,acthp/ucsc-xena-server,ucscXena/ucsc-xena-server,ucscXena/ucsc-xena-server,ucscXena/ucsc-xena-server,acthp/ucsc-xena-server,acthp/ucsc-xena-server,acthp/ucsc-xena-server