Before this commit, when defining a getter in the env passed to useSubEnv,
the value was read, losing the definition of the property.
After this commit, declaring a getter in the env works as expected:
the property stays a getter.
t-out automatically escaped content when it is a string not marked
with the `markup` function
t-out renders the raw content if it is a Block, or if it has been marked
with the `markup` funtion.
t-esc has been kept since it is safe and is optimized to render text nodes.
all t-raw calls are in fact the same as t-out.
Géry Debongnie