Fix English mistakes

• Fixed typography especially relating to spaces before colons. In English as opposed to French, there are no spaces before a punctuation mark.
• Fixed translation of "priorité". In the context of operators, English uses the word "precedence".
• The use of the term "double number" is unclear. If this is referring to the double type, it should be written in code font, otherwise it could be confused with meaning two distinct numbers entered one after the other without an operator in between. If this is referring to numbers with a decimal point and digits in decimal places, then I suggest using the term "decimal number". This is more consistent with the user experience, and the details on the limitations of such decimal numbers is well documented in one of the sections.