Documentation improvements to libmodbus page

doc/libmodbus.txt

@@ -107,36 +107,49 @@ are provided to modify and free a 'context':
 Free libmodbus context::
     linkmb:modbus_free[3]
 
-Context setters and getters::
+Set slave ID::
+    linkmb:modbus_set_slave[3]
+
+Enable debug mode::
+    linkmb:modbus_set_debug[3]
+
+Timeout settings::
     linkmb:modbus_get_byte_timeout[3]
     linkmb:modbus_set_byte_timeout[3]
-    linkmb:modbus_set_debug[3]
-    linkmb:modbus_set_error_recovery[3]
-    linkmb:modbus_get_header_length[3]
     linkmb:modbus_get_response_timeout[3]
     linkmb:modbus_set_response_timeout[3]
-    linkmb:modbus_set_slave[3]
+
+Error recovery mode::
+    linkmb:modbus_set_error_recovery[3]
+
+Setter/getter of internal socket::
     linkmb:modbus_set_socket[3]
     linkmb:modbus_get_socket[3]
 
+Information about header::
+    linkmb:modbus_get_header_length[3]
+
 A libmodbus 'context' is thread safe and may be shared among as many application
 threads as necessary, without any additional locking required on the part of the
 caller.
 
 Macros for data manipulation::
-    MODBUS_GET_HIGH_BYTE(data), extracts the high byte from a byte
-    MODBUS_GET_LOW_BYTE(data), extracts the low byte from a byte
-    MODBUS_GET_INT32_FROM_INT16(tab_int16, index), builds an int32 from the two
-    first int16 starting at tab_int16[index]
-    MODBUS_GET_INT16_FROM_INT8(tab_int8, index), builds an int16 from the two
-    first int8 starting at tab_int8[index]
-    MODBUS_SET_INT16_TO_INT8(tab_int8, index, value), set an int16 value into
-    the two first bytes starting at tab_int8[index]
-
-Functions for data manipulation::
+
+- MODBUS_GET_HIGH_BYTE(data), extracts the high byte from a byte
+- MODBUS_GET_LOW_BYTE(data), extracts the low byte from a byte
+- MODBUS_GET_INT32_FROM_INT16(tab_int16, index), builds an int32 from the two
+  first int16 starting at tab_int16[index]
+- MODBUS_GET_INT16_FROM_INT8(tab_int8, index), builds an int16 from the two
+  first int8 starting at tab_int8[index]
+- MODBUS_SET_INT16_TO_INT8(tab_int8, index, value), set an int16 value into
+  the two first bytes starting at tab_int8[index]
+
+Handling of bits and bytes::
     linkmb:modbus_set_bits_from_byte[3]
     linkmb:modbus_set_bits_from_bytes[3]
     linkmb:modbus_get_byte_from_bits[3]
+
+Set or get float numbers::
     linkmb:modbus_get_float[3]
     linkmb:modbus_set_float[3]
     linkmb:modbus_get_float_swapped[3]