Support alpha, beta and rc

[omid]

After deployment of this ticket, gitversion command should accept the following attributes:

• -alpha-keyword keyword
• -beta-keyword keyword
• -rc-keyword keyword

For example:
gitversion -alpha-keyword alpha -beta-keyword b -rc-keyword rc

And type can have the following values:

• alpha
• beta
• rc

The changes will be like the following matrix:

Old Version	Type	New Version
v1.2.3	alpha	v1.2.4-alpha
v1.2.4-alpha	alpha	v1.2.4-alpha.1
v1.2.4-alpha.1	alpha	v1.2.4-alpha.2
v1.2.4-alpha	beta	v1.2.4-beta
v1.2.3	beta	v1.2.4-beta
v1.2.3	rc	v1.2.4-rc