sancus.text: new namespace for encoders/decoders
sancus.text.xml: add dummy NOP XML encoder/decoder

Signed-off-by: Alejandro Mery <amery@geeks.cl>
sancus.text.json: add dummy NOP JSON encoder/decoder

Signed-off-by: Alejandro Mery <amery@geeks.cl>
sancus.text.html: add dummy NOP HTML encoder

Signed-off-by: Alejandro Mery <amery@geeks.cl>
text.html: import string and generic encoders from sancus.web