fixing mistakes and typos

Author: patriciogonzalezvivo

02/README.md

@@ -18,7 +18,7 @@ Although these simple lines of code don't look like a lot, we can infer substant
 
 4. If we look closely to the ```vec4``` type we can infer that the four arguments respond to the RED, GREEN, BLUE and ALPHA channels. Also we can see that these values are *normalized*, which means they go from ```0.0``` to ```1.0```. Later, we will learn how normalizing values makes it easier to *map* values between variables. 
 
-5. Another important *C feature* we can see in this example is the presence of preprocessor macros. Macros are part of a pre-compilation step. With them it is possible to ```#define``` global variables and do some basic conditional operation ( with ```#ifdef``` and ```#endif```). All the macro comands begin with a hastag (```#```). Pre-compilation happens right before compiling and copies all the calls to ```#defines``` and check ```#ifdef``` (is defined) and ```#ifndef``` (is not defined) conditionals. In our "hello world!" example above, we only insert the line 2 if ```GL_ES``` is defined, which mostly happens when the code is compiled on mobile devices and browsers.
+5. Another important *C feature* we can see in this example is the presence of preprocessor macros. Macros are part of a pre-compilation step. With them it is possible to ```#define``` global variables and do some basic conditional operation ( with ```#ifdef``` and ```#endif```). All the macro comands begin with a hashtag (```#```). Pre-compilation happens right before compiling and copies all the calls to ```#defines``` and check ```#ifdef``` (is defined) and ```#ifndef``` (is not defined) conditionals. In our "hello world!" example above, we only insert the line 2 if ```GL_ES``` is defined, which mostly happens when the code is compiled on mobile devices and browsers.
 
 6. Float types are vital in shaders, so the level of *precision* is crucial. Lower precision means faster rendering, but on behalf of quality. You can be picky and specify the precision of each variable that uses floating point. In the first line (```precision mediump float;```) we are setting all floats to medium precision. But we can choose to set them to low (```precision lowp float;```) or high (```precision highp float;```).
 

04/README.md

@@ -113,7 +113,7 @@ void draw() {
 }
 ```
 
-In the order for the shader to work, you need to add the following line at the beginning of your shader: ```#define PROCESSING_COLOR_SHADER```. So in Processing a shader looks like this:
+In the order for the shader to work on versions previus to 2.1, you need to add the following line at the beginning of your shader: ```#define PROCESSING_COLOR_SHADER```. So it looks like this:
 ```glsl
 #ifdef GL_ES
 precision mediump float;