Remove 'textauto' option

For the same reason we removed 'textmode'.
Remove "h" flag of 'highlight' option

HLF_H is an obsolete flag and got replaced by HLF_E.
Add the -Wconversion flag for some files.

This is to provide some infrastructure to help with issue #567 (Enable
-Wconversion file by file).
fix -Wconversion warnings for rstream

I'm not sure whether to go for signed or unsigned types for the offsets, but
without a doubt size_t is a better alternative than uint32_t. Added casts
after checking bounds before and after calling external libraries (in this
case libuv).
Remove dead code in clint.py