Option to skip first line in rec and 2 options to set custom bg and text color for export

[chiefMarlin]

Hi,
This pull request has 2 feature additions.

1. Added a parameter to rec command
   -s, --skip-first-line"
   This allows to skip the first line of recording
   Purpose of this is to allow user to set custom environment variables or change PS1 terminal variable before recording.
   Typical usage would be to set api key variables for the demo and to change usr@host PS1 variable.
   First line delimiter is set to \n and recording starts after [enter] is pressed
   Example:
   export API_KEY=test; PS1="user@host:"; some other command [enter]

• Recording starts

2. Added 2 parameters to export to allow setting custom background and text color for exported svg.
   -b, --background-color=STRING background color in hexadecimal format (e.g. #FFFFFF)
   -t, --text-color=STRING text color in hexadecimal format (e.g. #000000)
   This one is self explanatory, i find it very usefull to be able to customize what the svg will look like.

Thanks

[chiefMarlin]

Can we push this through @MrMarble