Fix few missing bold on error codes of the documentation

doc/modbus_mapping_new.txt

@@ -32,7 +32,7 @@ successful. Otherwise it shall return NULL and set errno.
 
 ERRORS
 ------
-ENOMEM::
+*ENOMEM*::
 Not enough memory
 
 

doc/modbus_read_bits.txt

@@ -32,7 +32,7 @@ successful. Otherwise it shall return -1 and set errno.
 
 ERRORS
 ------
-EMBMDATA::
+*EMBMDATA*::
 Too many bits requested
 
 

doc/modbus_read_input_bits.txt

@@ -32,7 +32,7 @@ input status if successful. Otherwise it shall return -1 and set errno.
 
 ERRORS
 ------
-EMBMDATA::
+*EMBMDATA*::
 Too many discrete inputs requested
 
 

doc/modbus_read_input_registers.txt

@@ -34,7 +34,7 @@ input registers if successful. Otherwise it shall return -1 and set errno.
 
 ERRORS
 ------
-EMBMDATA::
+*EMBMDATA*::
 Too many bits requested
 
 

doc/modbus_read_registers.txt

@@ -32,7 +32,7 @@ if successful. Otherwise it shall return -1 and set errno.
 
 ERRORS
 ------
-EMBMDATA::
+*EMBMDATA*::
 Too many registers requested
 
 

doc/modbus_reply.txt

@@ -33,7 +33,7 @@ successful. Otherwise it shall return -1 and set errno.
 
 ERRORS
 ------
-EMBMDATA::
+*EMBMDATA*::
 Sending has failed
 
 See also the errors returned by the syscall used to send the response (eg. send

doc/modbus_write_and_read_registers.txt

@@ -34,7 +34,7 @@ registers if successful. Otherwise it shall return -1 and set errno.
 
 ERRORS
 ------
-EMBMDATA::
+*EMBMDATA*::
 Too many registers requested, Too many registers to write
 
 

doc/modbus_write_bits.txt

@@ -29,7 +29,7 @@ successful. Otherwise it shall return -1 and set errno.
 
 ERRORS
 ------
-EMBMDATA::
+*EMBMDATA*::
 Writing too many bits